Radon lookup and county map

Radon Levels by Zip Code

Enter a zip code for your county's EPA radon zone, how many tested homes nearby came back at 4 pCi/L or higher, your state radon office and your state's radon disclosure rule. Built from EPA and CDC data, with zip-level results where states publish them.

Look Up My Zip See the Radon Map

What this combines

Official data only

EPA radon zones for 3,141 of 3,142 counties.
6.6 million home radon tests reported to the CDC by national labs and 22 state programs.
Zip-level results for 4,332 zip codes where 9 state agencies publish them.
Every state's radon office, plus its real-estate radon rule with the citation.

Radon varies house to house. These figures show the odds in your area; a test shows your home.

The short answer

Radon is measured in picocuries per liter (pCi/L). EPA says fix a home at 4 pCi/L or more and consider fixing between 2 and 4; the average US home is about 1.3. Of 2.0 million home radon tests that national labs reported to the CDC for 2008–2017, 36% came back at 4 or higher. Where you live changes the odds a lot: the typical county the EPA rates Zone 1 had 51% of its tests at 4+, against 9% in the typical Zone 3 county. A zip or county figure tells you how likely a problem is, not what your house has — only a test does.

Sources: EPA Map of Radon Zones and A Citizen’s Guide to Radon; CDC Environmental Public Health Tracking Network. Data downloaded September 30, 2026.

Radon map by county

Switch between the EPA’s radon zones (a 1993 prediction) and what testing has actually found: the share of tested homes at 4 pCi/L or more. Hover or tap a county for its figures; tap once to zoom to its state. Hatched counties have fewer than 30 tests, so read them as a hint.

Loading the county map…

Zone 1: predicted average greater than 4 pCi/L
Zone 2: predicted average 2 to 4 pCi/L
Zone 3: predicted average less than 2 pCi/L
Not listed

What the data shows

Radon by the numbers

Figures computed from the dataset behind the map; they update when the data does.

36%

of 2.0 million lab-reported home tests were at 4+ pCi/L

That is about 1 in 3 tests, far above EPA's national estimate of nearly 1 in 15 homes, because people who test are more likely to live where radon is common or to have a reason to check. A further 25% were in EPA's "consider fixing" band of 2 to 4.

51%

of tests at 4+ in the typical Zone 1 county

Against 31% in Zone 2 and 9% in Zone 3 (counties with 100+ tests). The 1993 zones still sort counties in the right order three decades on.

Zone 3 counties where a quarter or more of tests hit 4+

Low predicted potential is not low measured radon everywhere. King George County, VA (46%); Holt County, NE (43%); Herkimer County, NY (42%) are examples.

0.90

agreement between the two CDC test series

Across 795 counties with 30+ tests in both, the national-lab and state-program shares at 4+ correlate at 0.90. Statewide, Connecticut, Nebraska and Rhode Island differ by 10 points or more, so the lookup always shows both.

Counties where the most tests came back high

Counties with at least 100 tests, ranked by the share at 4 pCi/L or more.

County	EPA zone	Tests at 4+	Tests	Source, years
Clay County, NE	Zone 1	85%	194	National labs, 2008–2017
Sioux County, IA	Zone 1	84%	1,982	National labs, 2008–2017
Rock County, MN	Zone 1	84%	210	National labs, 2008–2017
Webster County, NE	Zone 1	83%	137	National labs, 2008–2017
Plymouth County, IA	Zone 1	82%	1,405	National labs, 2008–2017
O'Brien County, IA	Zone 1	82%	652	National labs, 2008–2017
Pickaway County, OH	Zone 1	81%	183	National labs, 2008–2017
York County, NE	Zone 1	80%	616	National labs, 2008–2017
Burt County, NE	Zone 1	80%	405	National labs, 2008–2017
Walsh County, ND	Zone 1	80%	132	National labs, 2008–2017
Clay County, IA	Zone 1	79%	744	National labs, 2008–2017
Butler County, NE	Zone 1	79%	483	National labs, 2008–2017
Nuckolls County, NE	Zone 1	79%	244	National labs, 2008–2017
Shelby County, IA	Zone 1	78%	857	National labs, 2008–2017
Audubon County, IA	Zone 1	78%	189	National labs, 2008–2017

Zone 3 counties that tested higher than their zone

County	Tests at 4+	Tests	Source
King George County, VA	46%	488	National labs
Holt County, NE	43%	349	National labs
Herkimer County, NY	42%	337	National labs
Maury County, TN	39%	509	National labs
Tuscola County, MI	36%	369	National labs
Garfield County, NE	33%	194	State program
Caroline County, VA	33%	199	National labs
Richmond city, VA	28%	520	National labs
Lincoln County, NE	27%	895	National labs
Henrico County, VA	27%	607	National labs
Huron County, MI	27%	260	National labs
Fredericksburg city, VA	26%	375	National labs

Zone 3 counties with 100+ tests where 25% or more were at 4 pCi/L or higher. 21 counties in all; the top 12 are shown.

Radon zone map, tested

Do the EPA radon zones match real test results?

The EPA Map of Radon Zones dates from 1993. It is a prediction of each county’s average indoor screening level, built from geology, aerial radioactivity, soil permeability, house construction and the limited indoor data of the time. It was never a measurement, and EPA’s own advice is to test no matter where you live. The question worth asking is whether it still sorts counties sensibly, and the test data says it does: the typical Zone 1 county had about 6 times the share of high tests of the typical Zone 3 county.

EPA zone	Counties in zone	Typical county: tests at 4+	Middle half of counties	Counties with 100+ tests
Zone 1	1,071	51%	39%–62%	731
Zone 2	1,034	31%	21%–40%	504
Zone 3	1,036	9%	4%–15%	189

Measured figures use each county's headline series (national labs 2008–2017 where they have 30+ tests, otherwise the state program), counties with 100+ tests only.

Reading a result

What radon levels mean

EPA says no level of radon is known to be safe. For a specific result, including the test type and EPA's next step, see what your radon test number means.

Level (pCi/L)	What EPA says	Never smoked: per 1,000	Smokers: per 1,000
4 or more	Fix your home	About 7 at 4 pCi/L	About 62 at 4 pCi/L
2 to 4	Consider fixing; below 2 is hard to reach	About 4 at 2 pCi/L	About 32 at 2 pCi/L
1.3	Average indoor level in US homes	About 2	About 20
0.4	Average outdoor level	–	About 3

Lung cancer risk figures are EPA's estimates for lifetime exposure at each level (people per 1,000 who could get lung cancer). Source: EPA, Health Risk of Radon.

EPA estimates radon causes about 21,000 lung cancer deaths a year in the US and is the leading cause among people who have never smoked. The risk comes from years of exposure, which is why EPA’s decisions rest on a home’s long-term average rather than a single high day.

Test, then fix

What to do about radon in your home

1. Test the right way

Short-term tests stay in the house 2 to 90 days: charcoal canisters, electret ion chambers, alpha-track or continuous monitors. Long-term tests run more than 90 days and are a better guide to the year-round average, because radon rises and falls day to day and season to season.
Put the kit in the lowest level you use regularly (the basement if you spend time there), not in a kitchen, bathroom or laundry, and keep windows and outside doors closed for short tests.
If a short-term test reads 4 pCi/L or more, follow up with a long-term test, or a second short-term test if you need an answer quickly, and act on the average.
Buying or selling? EPA’s real-estate guide allows two simultaneous short-term tests, two back-to-back tests, or a continuous monitor for at least 48 hours, with steps to prevent tampering, in the lowest level a buyer could use.

2. Fix it if it’s high

The standard fix is sub-slab depressurization: a pipe through the basement floor or slab and an in-line fan that pulls soil gas from under the floor and vents it above the roof. Crawl spaces get sub-membrane depressurization: sealed plastic over the ground with the same fan-and-pipe suction beneath it.
Sealing alone is not a fix. EPA does not recommend it because it has not been shown to lower radon significantly or consistently, but sealing floor cracks and fitting a gasketed sump lid makes an active system work better.
Typical cost: $1,500 to $3,000 per the Minnesota Department of Health; other state programs quote ranges starting from about $750. EPA says it is about the cost of other common home repairs. The fan adds a little to the electric bill. Our radon mitigation cost calculator compares every state and extension figure and works out the fan’s running cost.
Hire a mitigator licensed by your state (many states license them, see the table below) or certified by a national proficiency program. Retest no sooner than 24 hours and within 30 days after the system starts, then every two years, as EPA advises.

Radon by state

Radon levels, radon offices and disclosure laws by state

County zones, the share of tests at 4+ pCi/L, and each state’s real-estate radon rule. Pick a state on the map above to see every county.

Radon zones, measured test results, state radon offices and disclosure rules by state
State	Counties by zone (1 / 2 / 3)	Lab tests at 4+ (2008–2017)	State program tests at 4+	Home-sale radon rule	State radon office
Alabama	13 / 33 / 21	22% of 12,569	–	None foundSource	Alabama Department of Public Health, Office of Radiation Control - Radon Program(334) 290-6244; in-state toll-free 1-800-582-1866
Alaska	0 / 5 / 23	18% of 830	18% of 1,8422013–2022	On the mandatory disclosure formAS 34.70.010-.200; form adopted by 12 AAC 64.930Source	University of Alaska Fairbanks Cooperative Extension Service - Radon Program (state radon program)1-800-478-8324 (radon hotline)
Arizona	0 / 15 / 0	17% of 3,589	–	None foundSource	Arizona Department of Health Services, Bureau of Radiation Control - Radon Program602-542-1025
Arkansas	0 / 14 / 61	23% of 668	–	None foundSource	Arkansas Department of Health, Environmental Epidemiology - Radon Program501-661-2621
California	2 / 29 / 27	10% of 9,415	–	On the mandatory disclosure formCal. Civ. Code 1102.6 (TDS item C.1)Source	California Department of Public Health - Indoor Radon Program1-800-745-7236
Colorado	53 / 11 / 0	47% of 96,367	43% of 212,5292014–2023	Required by statuteC.R.S. 38-35.7-112 (SB 23-206)Source	Colorado Department of Public Health and Environment (CDPHE) - Radon Program1-800-846-3986 (Colorado Radon Hotline)
Connecticut	4 / 3 / 1	27% of 25,572	42% of 38,4632010–2019	On the mandatory disclosure formConn. Gen. Stat. 20-327bSource	Connecticut Department of Public Health - Radon Program(860) 509-7300
DelawareZip-level data	0 / 1 / 2	17% of 12,214	–	Required by statute6 Del. C. 2572ASource	Delaware Division of Public Health - Radon Office (Health Systems Protection)1-800-464-HELP (4357)
District of ColumbiaZip-level data	0 / 0 / 1	9% of 2,126	–	None foundD.C. Code 42-1305 (no radon item); 17 DCMR 2708 (unverified)SourceNot fully confirmed from primary text.	DC Department of Energy and Environment (DOEE) - Radon Program(202) 535-2302 (radon hotline)
Florida	0 / 9 / 58	23% of 53,794	23% of 176,0572014–2023	Required by statuteFla. Stat. 404.056(5)Source	Florida Department of Health - Radon and Indoor Air Quality Program1-800-543-8279 (radon hotline); 850-245-4288
Georgia	4 / 55 / 100	25% of 30,152	–	None foundSource	Georgia Radon Program (University of Georgia Cooperative Extension)
Hawaii	0 / 0 / 5	No lab data	–	None foundHRS ch. 508D (no radon-specific provision found)Source	Hawaii Department of Health, Indoor and Radiological Health Branch(808) 586-4700
IdahoZip-level data	19 / 20 / 5	42% of 12,961	–	None foundIdaho Code 55-2501 et seq. (no radon provision found)Source	Idaho Radon Program (Idaho Dept. of Health and Welfare, Environmental Health Program)1-800-445-8647
Illinois	56 / 43 / 3	43% of 108,909	36% of 837,1372008–2017	Required by statuteIllinois Radon Awareness Act, 420 ILCS 46Source	Illinois Emergency Management Agency and Office of Homeland Security (IEMA-OHS) Radon Program(800) 325-1245
Indiana	57 / 35 / 0	39% of 43,148	–	On the mandatory disclosure formIC 32-21-5; 876 IAC 9-1-1 (State Form 46234)Source	Indiana Department of Health, Lead & Healthy Homes Division (Radon)
IowaZip-level data	99 / 0 / 0	59% of 95,245	–	On the mandatory disclosure formIowa Code ch. 558A; Iowa Admin. Code 193E-14.1Source	Iowa Radon Program (Iowa HHS, Bureau of Radiological Health)1-800-383-5992
Kansas	65 / 40 / 0	No lab data	34% of 199,7612013–2022	Required by statuteK.S.A. 58-3078aSource	Kansas Radon Program (Kansas Dept. of Health and Environment, with Kansas State University)(800) 693-5343
Kentucky	30 / 82 / 8	44% of 28,793	–	On the mandatory disclosure formKRS 324.360; KREC Form 402Source	Kentucky Board of Radon Safety (the Dept. for Public Health radon program ended June 30, 2024)502-782-6782
Louisiana	0 / 0 / 64	2% of 499	2% of 16,0862013–2022	On the mandatory disclosure formLa. R.S. 9:3196-3200; LAC 46:LXVII-3601 (LREC 2026 Property Disclosure Document)Source	Louisiana Department of Environmental Quality, Radiation Section (radon)
Maine	12 / 4 / 0	38% of 11,825	–	Required by statute33 M.R.S. §173(4)(C)Source	Maine CDC Radiation Control Program (Radon)207-287-5676
Maryland	8 / 9 / 7	24% of 47,941	–	On the mandatory disclosure formMd. Code, Real Property §10-702Source	Maryland Department of the Environment Radon Program / Maryland Department of Health Environmental Health1-866-703-3266
Massachusetts	3 / 10 / 1	24% of 234,152	–	None found	Massachusetts Department of Public Health, Radiation Control Program - Radon Unit
MichiganZip-level data	9 / 32 / 42	27% of 114,407	–	On the mandatory disclosure formMCL 565.957 (Seller Disclosure Act, 1993 PA 92), item 10 Environmental ProblemsSource	Michigan EGLE Indoor Radon Program800-723-6642 (800-RADONGAS)
Minnesota	68 / 19 / 0	43% of 130,912	37% of 289,7342014–2023	Required by statuteMinn. Stat. 144.496Source	Minnesota Department of Health Indoor Air Unit - Radon Program651-201-4601
Mississippi	0 / 8 / 74	No lab data	–	On the mandatory disclosure formMiss. Code Ann. 89-1-501 et seq.; MREC Property Condition Disclosure StatementSource	Mississippi State Department of Health Radon Program (Indoor Radon Awareness)1-800-626-7739
Missouri	11 / 97 / 7	31% of 58,525	34% of 21,3602014–2023	None foundSource	Missouri Department of Health and Senior Services Radon Program (Environmental Epidemiology)573-751-6102 or 866-628-9891
Montana	49 / 7 / 0	46% of 9,893	–	Required by statuteMont. Code Ann. 75-3-606Source	Montana DEQ Radon Control Program1-800-546-0483
Nebraska	53 / 24 / 16	59% of 42,782	46% of 471,8142014–2023	On the mandatory disclosure formNeb. Rev. Stat. 76-2,120; 302 NAC 1 (Seller Property Condition Disclosure Statement)Source	Nebraska DHHS Radon Program (Indoor Air)402-471-0386
Nevada	9 / 7 / 1	23% of 10,930	–	On the mandatory disclosure formNRS 113.120-113.130; NV Real Estate Division Form 547 item 6(a)Source	Nevada Radon Education Program (University of Nevada, Reno Extension, under sub-grant from Nevada DPBH Radiation Control Program)775-336-0252
New Hampshire	1 / 9 / 0	35% of 15,608	40% of 9,6982012–2021	Required by statuteN.H. RSA 477:4-aSource	New Hampshire DHHS Radon Program
New Jersey	7 / 11 / 3	No lab data	12% of 1,030,9232013–2022	Required by statuteN.J.S.A. 26:2D-73Source	NJ Department of Environmental Protection Radon Section (Radiation Protection Element)1-800-648-0394
New Mexico	7 / 26 / 0	28% of 3,721	–	None foundSource	New Mexico Environment Department, Radiation Control Bureau - Indoor Radon Outreach Program505-476-8600
New York	34 / 13 / 15	25% of 97,145	24% of 26,9652014–2023	On the mandatory disclosure formN.Y. Real Property Law § 462 (Property Condition Disclosure Statement, Q.24)Source	New York State Department of Health Radon Program (Bureau of Environmental Radiation Protection)518-402-7556
North Carolina	8 / 31 / 61	23% of 73,139	21% of 41,0272013–2022	On the mandatory disclosure formN.C.G.S. § 47E-4; NCREC form REC 4.22 (Q.25)Source	North Carolina Radon Program (NCDHHS, Radiation Protection Section)1-800-662-7030
North Dakota	53 / 0 / 0	59% of 6,607	–	Required by statuteN.D. Cent. Code § 47-10-02.2 (2025 S.B. 2204)Source	North Dakota Department of Environmental Quality Radon Program (Division of Waste Management)701-328-5166
Ohio	53 / 35 / 0	52% of 98,840	–	On the mandatory disclosure formOhio Rev. Code § 5302.30Source	Ohio Department of Health Radon Education and Licensing Program614-728-0272
Oklahoma	0 / 9 / 68	13% of 814	–	On the mandatory disclosure form60 Okla. Stat. § 831 et seq. (Residential Property Condition Disclosure Act); OREC Appendix A formSource	Oklahoma Department of Environmental Quality Radon Program (Land Protection Division, Radiation Management)405-702-5100
OregonZip-level data	0 / 21 / 15	25% of 23,951	21% of 47,3882014–2023	On the mandatory disclosure formORS 105.464 (Q9.F); ORS 105.848Source	Oregon Radon Awareness Program (Oregon Health Authority)971-673-0440
PennsylvaniaZip-level data	49 / 17 / 1	42% of 203,045	35% of 882,9712011–2020	On the mandatory disclosure form68 Pa.C.S. § 7304(14); 49 Pa. Code § 35.335aSource	Pennsylvania DEP Bureau of Radiation Protection, Radon Division1-800-237-2366 (1-800-23-RADON)
Rhode Island	2 / 2 / 1	24% of 37,874	3% of 7,9012009–2018	Required by statuteR.I. Gen. Laws § 5-20.8-2(b)(3)(xii)Source	Rhode Island Department of Health Radon Control Program401-222-5960
South Carolina	1 / 8 / 37	19% of 26,481	–	On the mandatory disclosure formS.C. Code Ann. § 27-50-40(A)(6)Source	South Carolina Department of Environmental Services Radon Program (Bureau of Air Quality)1-800-768-0362
South Dakota	48 / 18 / 0	59% of 6,275	–	On the mandatory disclosure formS.D. Codified Laws 43-4-37 to 43-4-44 (form at 43-4-44)Source	South Dakota DANR Radon Program (Air Quality Program, Dept. of Agriculture and Natural Resources)1-800-438-3367
Tennessee	39 / 32 / 24	33% of 31,066	24% of 11,9842014–2023	On the mandatory disclosure formTenn. Code Ann. 66-5-202; form at 66-5-210Source	Tennessee Radon Program (TDEC)1-800-232-1139
Texas	0 / 39 / 215	10% of 4,615	–	On the mandatory disclosure formTex. Prop. Code 5.008 (TREC form OP-H / 55-1)Source	Texas Radon Group, Texas Tech University (took over the state radon program from Texas DSHS)806-834-0370
UtahZip-level data	7 / 22 / 0	42% of 28,342	38% of 109,2962014–2023	On the mandatory disclosure formNo statute found; seller property condition disclosure form as described by Utah DEQSourceNot fully confirmed from primary text.	Utah Radon Program, Division of Waste Management and Radiation Control (Utah DEQ)(801) 536-0091
Vermont	0 / 12 / 2	22% of 10,600	18% of 17,6012014–2023	None foundSource	Vermont Department of Health Radon Program802-863-7220 / 800-439-8550 (toll-free in VT)
Virginia	62 / 28 / 43	30% of 53,199	–	Required by statuteVa. Code 55.1-703Source	Virginia Department of Health Indoor Radon Program (Office of Radiological Health)(804) 864-8161
Washington	7 / 14 / 18	26% of 8,201	19% of 33,7922011–2020	On the mandatory disclosure formRCW 64.06.020Source	Washington State Department of Health Radon Program360-236-3200
West Virginia	20 / 29 / 6	38% of 10,061	–	None foundSource	West Virginia OEHS Radon Program (Radiation, Toxics & Indoor Air Division)(304) 352-5039
WisconsinZip-level data	28 / 44 / 0	47% of 68,104	42% of 149,9892014–2023	On the mandatory disclosure formWis. Stat. 709.02-709.03Source	Wisconsin Radon Program (Department of Health Services) and Regional Radon Information Centers1-888-569-7236 (1-888-LOW-RADON)
Wyoming	21 / 2 / 0	44% of 7,638	–	None foundSource	Wyoming Department of Health Radon Program (Wyoming Cancer Program)(307) 777-7656 / 1-800-264-1296

Each state’s radon rules in full

Alabama

Home sales: No Alabama statute or state-mandated seller disclosure form requiring radon disclosure was found; Alabama has no statutory seller disclosure form (buyer-beware state), so buyers should test on their own.

Alaska

Home sales: Sellers must give buyers the state Residential Real Property Transfer Disclosure Statement, which asks whether the seller is aware of environmental hazards including radon gas; there is no separate radon warning or test requirement.

Arizona

Home sales: No Arizona statute requiring radon disclosure was confirmed; the commonly used Seller's Property Disclosure Statement (SPDS) is a Realtor-association form rather than a statutory state form, so no confirmed legal requirement.

Arkansas

Home sales: No Arkansas radon disclosure law was found; the state health department's program material cites no state radon statute, and ADH does not certify or license radon testers or mitigators.

California

Home sales: Sellers of 1-4 unit homes must give the statutory Real Estate Transfer Disclosure Statement, which asks whether the seller is aware of environmental hazards 'such as... radon gas'; no radon test or separate radon warning is required.

Other radon laws: Anyone providing radon services to the public must hold NRPP (NEHA) or NRSB certification and register it with CDPH (Cal. Health & Safety Code 106750-106795).

Colorado

Home sales: Every residential sale contract must carry a bold-type statutory radon warning, and the seller must disclose any known radon test results, mitigation and mitigation systems and give the buyer the CDPHE radon real-estate brochure (in force for contracts from August 2023).

Other radon laws: Landlords must give tenants a signed radon warning, known test/mitigation information and the CDPHE brochure before a lease is signed, and failure (or failure to mitigate within 180 days of a 4 pCi/L+ result) breaches the warranty of habitability (C.R.S. 38-12-803 and 38-12-503(2.4), SB 23-206); Colorado also licenses radon measurement and mitigation professionals (C.R.S. Title 12, Article 165).

Connecticut

Home sales: Sellers must give buyers the state Residential Property Condition Disclosure Report before a contract is signed, and it asks whether a radon test was performed (attach the report), whether a radon control system is in place, and whether one was in place in the prior 12 months.

Other radon laws: Public schools serving grades K-12 must test for radon in indoor air (Conn. Gen. Stat. 10-220(d)).

Delaware

Home sales: Buyers of residential property must be notified that the property may present radon exposure, the seller must hand over any radon test/inspection information and disclose known radon hazards on a Real Estate Commission radon form, and the selling broker must provide the DHSS radon information pamphlet.

District of Columbia

Home sales: The DC seller disclosure statute lists no radon item; the widely used DC Seller's Disclosure Statement (an association form tied to 17 DCMR 2708) asks about hazards including radon gas, but the official regulatory form text could not be verified, so no confirmed radon requirement.

Other radon laws: No one may perform radon screening, testing or mitigation for a fee in DC unless EPA-listed or certified by an approved proficiency organization (D.C. Code 28-4201).

Florida

Home sales: A statutory 'RADON GAS' notification statement must appear on at least one document signed at or before a contract to buy or a rental agreement for any building (short stays of 45 days or less excepted); no test or mitigation is required.

Other radon laws: The same notice applies to residential leases; Florida certifies radon measurement and mitigation businesses and individuals (Fla. Stat. 404.056(2)); and K-12 schools, state 24-hour care facilities and licensed day care centers in intermediate/elevated radon-potential counties must test (Fla. Stat. 404.056(4)).

Georgia

Home sales: The state radon program says Georgia law does not require radon testing or mitigation in most real estate transactions, and no radon disclosure statute was found.

Hawaii

Home sales: Hawaii's mandatory seller disclosure law (HRS ch. 508D) requires disclosure of material facts generally but no section names radon; the radon line on the common Seller's Real Property Disclosure Statement is from the REALTORS form, not state-mandated text.

Idaho

Home sales: The statutory Property Condition Disclosure Form in Idaho Code 55-2508 does not mention radon (checked full chapter text); the Idaho REALTORS RE-25 form asks about radon but is not state-mandated.

Illinois

Home sales: Before the buyer is obligated under a contract, the seller must give the buyer the IEMA pamphlet 'Radon Testing Guidelines for Real Estate Transactions' and the 'Illinois Disclosure of Information on Radon Hazards', which carries a radon warning statement and the seller's disclosure of any known elevated radon levels and test records.

Other radon laws: Landlords must give tenants in units below the third floor a radon pamphlet, any existing test results and a radon hazards disclosure (420 ILCS 46). Radon testers and mitigators must be licensed by IEMA-OHS (Radon Industry Licensing Act, 420 ILCS 44). All new homes must include passive radon-resistant construction (Radon Resistant Construction Act, 420 ILCS 52).

Indiana

Home sales: Sellers of 1-4 unit homes must give buyers the state Seller's Residential Real Estate Sales Disclosure (State Form 46234), whose Hazardous Conditions question asks whether there have been hazardous conditions such as 'radon gas in house or well'.

Other radon laws: Radon testers, mitigators and labs must be licensed by the Indiana Department of Health (410 IAC 5.1).

Iowa

Home sales: The Real Estate Commission's mandatory seller disclosure statement asks about any known radon tests (date and results), and the seller and buyer acknowledge the buyer is given the 'Iowa Radon Home-Buyers and Sellers Fact Sheet'.

Other radon laws: Public school districts must radon-test every attendance center by July 1, 2027 and every five years after, publish results, mitigate at 4 pCi/L or higher, and build new schools radon-resistant (Iowa Code 280.32); radon testers, mitigators and labs must be state-certified (Iowa Code 136B; 641 IAC 43).

Kansas

Home sales: Every residential real estate sales contract must include a statutory radon statement warning the buyer about indoor radon and lung cancer, recommending testing by a certified technician, and requiring the seller to disclose any known elevated radon readings.

Other radon laws: Anyone performing radon testing or mitigation must be certified by KDHE (Radon Certification Law, K.S.A. 48-16a01 to 48-16a12).

Kentucky

Home sales: The mandatory KREC Seller's Disclosure of Property Condition (Form 402) has a Radon Disclosure section asking whether the seller knows of radon testing and its results, and whether a radon mitigation system is installed and working.

Other radon laws: Radon measurement, mitigation and lab work requires state certification overseen by the Kentucky Board of Radon Safety (KRS 309.430 to 309.454; formerly cited as KRS 211.9101 to 211.9135).

Louisiana

Home sales: Sellers must complete the Louisiana Real Estate Commission Property Disclosure Document, which asks whether the property contains 'Radon gas' (Yes/No/Not Known).

Maine

Home sales: The seller's written property disclosure statement must cover known hazardous materials, and the statute names radon specifically.

Other radon laws: Landlords must have residential buildings radon-tested by a state-registered tester (new buildings within 12 months of occupancy; retest every 10 years on tenant request) and give tenants written results; either party may end the lease at 4.0 pCi/L or higher (14 M.R.S. §6030-D). Only owners/occupants or state-registered providers may test or mitigate radon, and homes being sold must use registered providers (Radon Registration Act, 22 M.R.S. ch. 165).

Maryland

Home sales: Sellers of 1-4 unit homes must give buyers either a disclaimer statement or a disclosure statement, and the statute requires the disclosure statement to cover known 'hazardous or regulated materials, including ... radon'.

Massachusetts

Home sales: No Massachusetts statute requiring radon disclosure, notice, or testing in residential sales was found; Massachusetts has no state-mandated seller disclosure form.

Michigan

Home sales: The Seller Disclosure Act's statutory disclosure statement asks sellers whether they are aware of environmental hazards 'such as ... asbestos, radon gas, formaldehyde, lead-based paint', answered unknown/yes/no; there is no radon-specific warning, pamphlet, or testing requirement.

Minnesota

Home sales: Under the Minnesota Radon Awareness Act, before a buyer signs a purchase agreement the seller must give a written statutory radon warning, disclose known radon test results and any mitigation system, and provide the MDH publication 'Radon in Real Estate Transactions'; buyers may sue within two years for non-disclosure.

Other radon laws: Radon measurement and mitigation professionals, mitigation companies and labs must be licensed annually by MDH, with system tags required on mitigation systems installed after 2019 (Minn. Stat. 144.4961); the Minnesota Residential Code requires passive radon control in new homes statewide (Minn. R. 1303.2400).

Mississippi

Home sales: Mississippi's statutory Property Condition Disclosure Statement (for 1-4 unit residential sales) asks whether the seller is aware of hazardous conditions or substances including radon gas; there is no radon-specific warning or testing requirement.

Missouri

Home sales: No enacted Missouri statute requiring radon disclosure in real estate sales was found (radon disclosure bills such as SB 417/SB 720 were introduced but not confirmed enacted); DHSS says Missouri has no radon testing regulations, and the seller's disclosure form it refers to is not state-mandated.

Montana

Home sales: A statutory radon gas warning must appear on at least one document signed before or with an offer to buy habitable property, the buyer must sign an acknowledgment of it, and a seller who knows the building was tested must provide the test results and evidence of any mitigation.

Nebraska

Home sales: The Nebraska Real Estate Commission's mandated Seller Property Condition Disclosure Statement asks whether the seller knows of radon gas identified by EPA or its Nebraska designee and whether the structures have been mitigated for radon; there is no separate radon warning or testing requirement.

Other radon laws: Anyone providing radon measurement or mitigation services in Nebraska must be licensed by DHHS (Neb. Rev. Stat. 71-3503 et seq., Radiation Control Act; 180 NAC 11).

Nevada

Home sales: The Seller's Real Property Disclosure Form required by NRS 113.130 (Real Estate Division Form 547) asks whether the seller knows of environmental hazards including radon gas; NRS chapter 113 itself does not mention radon and there is no radon-specific warning or testing requirement.

New Hampshire

Home sales: Before a purchase contract for property with a building is signed, the seller or seller's agent must give the buyer a statutory radon notice (radon may enter through soil or deep-well water; testing and removal equipment are available), and the buyer must sign a copy acknowledging receipt.

New Jersey

Home sales: If a building has been radon tested, the seller must give the buyer a copy of the test results and evidence of any later mitigation when the sale contract is entered into, and a buyer who contracts for testing is entitled to the results.

Other radon laws: All businesses and individuals doing radon testing or mitigation must be DEP-certified (N.J.A.C. 7:28-27), and the Radon Hazard Subcode requires radon-resistant construction for new Use Group R and E buildings in Tier 1 municipalities (N.J.A.C. 5:23-10).

New Mexico

Home sales: No New Mexico statute or state-mandated seller disclosure form requiring radon disclosure was found; sellers and brokers fall under general adverse-material-fact disclosure rules.

Other radon laws: No state radon certification program exists (NMED says 'there is not currently a certification program within the state'); no school, rental or new-construction radon law confirmed.

New York

Home sales: The statutory Property Condition Disclosure Statement sellers must deliver asks 'Has a radon test been done?' and, if yes, to attach a copy of the report (question 24).

Other radon laws: The NYS Office of Children and Family Services requires radon testing as part of the environmental hazards assessment for licensed day care providers in certain areas of the state, and radon testers/mitigators must report results to DOH under 10 NYCRR Part 16 (16.130).

North Carolina

Home sales: Sellers must give buyers the NC Real Estate Commission's Residential Property and Owners' Association Disclosure Statement, whose question 25 on hazardous or toxic substances includes radon gas; no radon-specific statute.

Other radon laws: NC does not require radon testing or mitigation in any building, including schools and child care (NCDHHS:); Session Law 2023-91 (HB 782) directs creation of a Radon Proficiency Program for radon professionals, still in development.

North Dakota

Home sales: Since August 1, 2025, a seller of residential property must disclose in writing any knowledge of radon concentrations, give the buyer a statutory radon warning statement to sign, and hand over any prior radon test results and evidence of mitigation before the sale agreement.

Ohio

Home sales: Sellers of 1-4 unit residential property must deliver the state residential property disclosure form, which by statute must address hazardous materials including radon gas.

Other radon laws: Radon testers, mitigation specialists, mitigation contractors and laboratories must be licensed by the Ohio Department of Health under Ohio Rev. Code Chapter 3723 and Ohio Adm. Code 3701-69.

Oklahoma

Home sales: Sellers must deliver the Oklahoma Real Estate Commission's Residential Property Condition Disclosure Statement, which asks whether the seller is aware of radon gas (Q25) and whether the property has been tested for radon (Q26).

Oregon

Home sales: The statutory seller's property disclosure statement asks whether any part of the property has been tested or treated for radon gas (Q9.F), and the Real Estate Agency must publish radon information for buyers of one- and two-family homes.

Other radon laws: School districts must test frequently occupied school rooms for radon and make results public (ORS 332.166-332.167), and radon-resistant construction is required for new homes and public buildings in Baker, Clackamas, Hood River, Multnomah, Polk, Washington and Yamhill counties (ORS 455.365).

Pennsylvania

Home sales: The Real Estate Seller Disclosure Law requires a disclosure form covering the presence of hazardous substances, and the Commission's mandated Seller Property Disclosure Statement expressly lists radon in that question.

Other radon laws: Anyone other than the building owner who performs radon testing, mitigation or lab analysis must be certified by DEP under the Radon Certification Act (63 P.S. § 2001 et seq.) and 25 Pa. Code Chapter 240.

Rhode Island

Home sales: The seller's written disclosure for 1-4 unit homes must include a radon item (test, company) and the statutory statement that radon exists in Rhode Island and testing before purchase is advisable.

Other radon laws: The Radon Control Act requires radon evaluation of public and 'high priority' buildings, defined to include pre-K-12 public, private and parochial schools, day care centers and nurseries (R.I. Gen. Laws §§ 23-61-3, 23-61-7), and requires radon testers and mitigators to be licensed/certified (§ 23-61-5).

South Carolina

Home sales: The statutory residential property condition disclosure statement must ask about the presence of environmental hazards including radon gas.

South Dakota

Home sales: Sellers of residential property must complete the statutory property condition disclosure statement, whose Hazardous Conditions section asks about existing conditions and tests performed for 'Radon Gas (House)' and 'Radon Gas (Well)'.

Tennessee

Home sales: Sellers of 1-4 unit residential property who use the statutory disclosure form must answer yes/no/unknown on whether they know of environmental hazards on the property, expressly including radon gas.

Texas

Home sales: Sellers of single-dwelling residential property must give buyers the statutory Seller's Disclosure Notice, which asks whether the seller is aware of 'Radon Gas' among other conditions; no testing is required.

Utah

Home sales: Utah DEQ states sellers must answer the seller property condition disclosure question 'Are there any hazardous conditions on the Property such as Radon gas in house or well?' (Yes/No/Do Not Know); no Utah statute mandating radon disclosure was found, so this rests on the standard disclosure form DEQ describes.

Vermont

Home sales: The Vermont Department of Health states that Vermont law does not require a radon test as part of a real estate transaction; no radon disclosure statute was found.

Other radon laws: Every public and approved independent school had to perform an ANSI/AARST MALB radon measurement on facilities not tested in five years and share the results with staff and students (2021 Vt. Acts No. 72, Sec. 12; deadline later extended to June 30, 2025).

Virginia

Home sales: The required residential property disclosure statement must tell buyers the owner makes no representation about whether the property is in an EPA radon Zone 1 or Zone 2 and advise them to do their own due diligence, such as checking EPA's radon zone map or ordering a radon inspection.

Other radon laws: Every public school building must be tested for radon under EPA procedures with results kept on file and reported to the Health Department (Va. Code 22.1-138), and radon testers/mitigators must be NRPP- or NRSB-listed (or meet Board of Health/EPA standards) and follow EPA/ASTM standards (Va. Code 32.1-229.01).

Washington

Home sales: Sellers must give buyers the statutory seller disclosure statement, which asks whether there are environmental-concern substances on the property 'such as asbestos, formaldehyde, radon gas, lead-based paint'.

Other radon laws: The state residential code requires radon-resistant new construction (IRC Appendix AF) in the high-radon-potential counties Clark, Ferry, Okanogan, Pend Oreille, Skamania, Spokane and Stevens, and for unvented-crawl-space buildings elsewhere (WAC 51-51-60101).

West Virginia

Home sales: No West Virginia statute requiring radon disclosure in residential real estate transactions was found.

Other radon laws: Radon testers, mitigation specialists, mitigation contractors and radon laboratories must be state-licensed (W. Va. Code 16-34-1 et seq., rules at 64CSR78), and new public school buildings must be radon-tested within a year of occupancy and at least every five years after, with mitigation if levels exceed standards (W. Va. Code 18-9E-3).

Wisconsin

Home sales: Sellers of 1-4 unit residential property must complete the statutory Real Estate Condition Report, which asks whether the owner knows of a defect caused by unsafe concentrations of radon (or radium in water supplies); testing is not required.

Wyoming

Home sales: No Wyoming statute requiring radon disclosure in real estate transactions was found (Wyoming has no statutory seller disclosure form, and the ELI 2025 radon law database lists no Wyoming radon laws).

Method and limits

Where these numbers come from

EPA radon zones. From EPA’s text version of the Map of Radon Zones (3,144 county rows), matched to Census county codes by name. 3140 rows matched. Where a 1993 area was later split (Alaska’s Wrangell-Petersburg and Prince of Wales-Outer Ketchikan), each successor keeps the original zone. Not assigned: Hoonah-Angoon Census Area, AK (02105). Rows for areas that no longer exist (Yellowstone National Park, MT, MT; Bedford city, VA; Clifton Forge city, VA; South Boston city, VA) are dropped.

Measured test results. Two series from the CDC Environmental Public Health Tracking Network. “Radon Tests from Labs” comes from national radon testing laboratories and covers 47 states and DC for 2008–2017 (2.0 million pre-mitigation tests, the latest 10-year window CDC serves). “Radon Tests from States” comes from 22 state radon programs, reported yearly; we pool each state’s latest 10 reported years (4.6 million tests). We add up the tests in CDC’s three bands (under 2, 2 to 4, 4 and over pCi/L) and compute shares; the county median and mean are CDC’s own figures. The map uses the lab series where a county has 30+ lab tests, because it is one method and one decade across state lines, and falls back to the state series. Shares are hidden under 10 tests.

Zip-level results. Where a state agency publishes radon results by zip code in a downloadable form, the lookup shows them for that zip (only zips with 10+ tests). Each publisher counts differently, so the card names the source and period:

Pennsylvania: Pennsylvania Department of Environmental Protection, 2016–2025; 1,447 zips, 1,097,504 tests. Test-level records; residential and unspecified buildings (schools and non-residential excluded). Pre- and post-mitigation tests are not distinguished in the source.
Wisconsin: Wisconsin Department of Health Services, years not stated by the publisher; 712 zips, 190,364 tests. Aggregated by DHS from private-lab results; the publisher does not state the years covered (file published March 2026).
Michigan: Michigan Department of Environment, Great Lakes, and Energy, rolling 10 years, per EGLE; 678 zips, 55,944 tests. First-time tests without an active mitigation system; EGLE counts results greater than 4 and greater than 2 pCi/L.
Iowa: Iowa Department of Health and Human Services, 2000–2024; 900 zips, 521,054 tests. All test purposes (real-estate and post-mitigation tests included); results reported by credentialed specialists and labs.
Oregon: Oregon Health Authority, Oregon Radon Awareness Program, 2024 edition, years not stated; 211 zips, 53,183 tests. Counts tested homes (locations) rather than tests; data from test-kit manufacturers.
Utah: Utah Department of Environmental Quality, 1990–2019; 179 zips, 63,829 tests. Short-term tests.
Idaho: Idaho Department of Health and Welfare, years not stated by the publisher; 202 zips, 45,811 tests. Share computed from the published count of tests over 3.9 pCi/L.
Delaware: Delaware Department of Health and Social Services, 2023–2025; 31 zips, 1,609 tests. Contractor reports and state-supplied home kits, October 2023 to October 2025.
District of Columbia: District of Columbia Department of Energy and Environment (DC GIS), 2023–2025; 15 zips, 790 tests. Summarised by zip from DC's published test records (813 tests, a few post-mitigation or real-estate).

We did not use California’s zip table (CDPH says it is not suitable for statistical or geospatial analysis), Maryland’s and Nevada’s (no count or share at 4 pCi/L), Tennessee’s (period and fields not defined), Rhode Island’s (mostly schools and public buildings) or Illinois’s test-level layer (undocumented validity flag); the county series covers those states. Other states publish only county, town or municipality figures, or dashboards without downloads. Zips are matched to counties with the Census 2020 ZCTA relationship file by land area; a zip covering 20% or more of another county shows that county too.

Limits. Tested homes are not a random sample: people test during home sales, after a neighbour finds radon, or because they live somewhere known for it, so shares run higher than EPA’s nearly-1-in-15 national estimate. CDC counts tests not marked pre- or post-mitigation as pre-mitigation, and Pennsylvania’s file does not mark them at all, which can pull shares down. State-program and lab figures disagree in some places (statewide by 10 points or more in Connecticut, Nebraska and Rhode Island), probably because they cover different buildings and years, so we show both. A county figure says nothing certain about one house.

The USGS 2025 Geologic Radon Potential map is the geology behind the EPA zones, drawn by geologic province rather than county, so it is not joined here. We did not use any radon company’s data.

FAQs

Radon levels by zip code: common questions

How do I find the radon level for my zip code?

Enter the zip in the lookup above. It returns the EPA radon zone for the county the zip sits in, the share of tested homes there that measured 4 pCi/L or more (from national labs and, in 22 states, the state radon program, both via the CDC), and zip-level test results where the state publishes them (Pennsylvania, Wisconsin, Michigan, Iowa, Oregon, Utah, Idaho, Delaware and District of Columbia). No source can give the level inside a particular house: radon varies from house to house on the same street, so the figure is a reason to test, not a substitute for one.

What is EPA radon Zone 1, Zone 2 and Zone 3?

The EPA Map of Radon Zones (1993) put every county into one of three zones by its predicted average indoor screening level: Zone 1 above 4 pCi/L (highest potential), Zone 2 from 2 to 4 (moderate), Zone 3 below 2 (low). The prediction combined geology, aerial radioactivity, soil permeability, foundation types and the indoor data available in the early 1990s. It is a prediction, not a measurement, and EPA's advice is to test your home no matter where you live.

Is Zone 3 safe from radon?

No. Zone 3 means low predicted potential, not zero. In the Zone 3 counties with at least 100 tests on record, the typical county still had 9% of tests at 4 pCi/L or more, and 21 Zone 3 counties had a quarter or more of their tests at that level. EPA recommends testing every home regardless of zone.

Which state has the highest radon levels?

By the share of home tests at 4 pCi/L or more reported by national labs for 2008–2017, the highest states were North Dakota (59%), Iowa (59%), Nebraska (59%), South Dakota (59%), Ohio (52%). Every county in Iowa, North Dakota is EPA Zone 1. Tested homes are not a random sample, so rankings describe the homes that were tested.

Is radon worse in a basement?

Usually, yes. Radon is a soil gas and enters through the parts of a house in contact with the ground: floor cracks, the wall-floor joint, sump pits, gaps around pipes. The lowest level is typically the highest reading. That is why EPA says to test in the lowest level you use regularly, and in a home sale, the lowest level a buyer could use.

Is it okay to sleep in a basement with radon?

It depends on the measured level, not on the room. If a long-term test, or two short-term tests, average 4 pCi/L or more in the basement, EPA's advice is to fix the house rather than avoid the room; a mitigation system lowers radon throughout the home. Below 4, EPA suggests considering a fix between 2 and 4, especially where people sleep or spend long hours.

Does finishing or waterproofing a basement reduce radon?

Not reliably. EPA does not recommend sealing alone as a radon fix because sealing has not been shown to lower radon significantly or consistently. Finishing can even hide entry points. Sealing cracks and fitting a gasketed sump lid do make an active radon system work better. Test before you finish a basement, and again after.

How much does radon mitigation cost?

The Minnesota Department of Health puts a typical radon mitigation system at $1,500 to $3,000 and warns against quotes under $1,000. EPA says a system costs about the same as other common home repairs, and the fan adds a small amount to the electric bill. Cost depends on the foundation (basement, slab, crawl space or a mix), how many suction points are needed and where the pipe can run.

Do crawl spaces have radon?

Yes. Radon comes up from the soil under a crawl space just as it does under a slab. EPA describes sub-membrane depressurization for crawl spaces: a sealed plastic sheet over the ground with a fan drawing soil gas from beneath it. A vapor barrier or encapsulation alone is not a radon system unless it is depressurized.

How accurate is a radon map by zip code?

A zip or county figure is an average over many different houses, soils and foundations, and it is only as good as the testing behind it. We show the number of tests and years for every figure, hatch areas with fewer than 30 tests, and hide percentages below 10 tests. The two CDC series agree closely (correlation 0.90 across 795 counties with both), but neither can tell you your own home's level.

Do I have to disclose radon when selling a house?

It depends on the state. We found radon-specific rules in state law or the state's mandatory disclosure form in 38 of 51 jurisdictions (the 50 states and DC). In 13 (Colorado, Delaware, Florida, Illinois, Kansas, Maine, Minnesota, Montana, New Hampshire, New Jersey, North Dakota, Rhode Island and Virginia) a radon statute sets the rule, usually a warning, pamphlet or disclosure of known results in every sale; in the rest it is a radon question on the state's mandatory seller disclosure form. The state table below lists each state's rule and citation.

Open data

Download the data and cite it

The county file has the EPA zone and both CDC series for all 3,142 counties, one row each. It is free to reuse under CC BY 4.0 with a link back to this page; see our terms of use.

Download CSV (185 KB)

How to cite

Wet Basement Fixes. “Radon Levels by Zip Code: EPA radon zones and measured test results by county.” Data from US EPA Map of Radon Zones and CDC Environmental Public Health Tracking Network, compiled September 30, 2026. https://www.wetbasementfixes.com/tools/radon-levels-by-zip-code

Sources

EPA and CDC data are public domain. Zip-level files are published by the state agencies listed in the method notes. State law entries were checked against statute text or the state agency's own page on September 30, 2026; laws change, so confirm with your state radon office before relying on one.