January is National Radon Action Month, and EPA's advice during it is blunt: "Test your home - EPA and the U.S. Surgeon General recommend that all homes in the U.S. be tested for radon. Testing is easy and inexpensive." Winter is also the practical season for short-term tests, which want closed windows and doors for the duration; EPA's Citizen's Guide instructions say so directly.

What Radon Zone Am I In?

Q: Can the map tell me whether my home has radon?

No. EPA's words: "The map should not be used to determine if a home in a given zone should be tested for radon. Homes with elevated levels of radon have been found in all three zones. All homes should be tested for radon." Zones describe counties; tests describe homes. The ZIP tool on this page reports your county's zone and then points you at how to run an actual test.

Q: Why does my ZIP code show more than one county?

Because ZIP codes are postal routes, not county lines, and about three in ten cross a county boundary. The tool shows every county your ZIP touches, with each county's share of the ZIP's land area, because the counties can sit in different zones and silently picking one would put some readers in the wrong zone.

Enter a ZIP code and get the real answer: every county the ZIP touches, each county's zone on the 1993 EPA Map of Radon Zones with EPA's definition and its test-every-home caveat attached, newer state test data where a state publishes any, and the exact doors to knock on to test.

EPA assigned 3,143 counties to three radon zones in 1993: 1,069 highest, 1,035 moderate, 1,039 low potential

Counties zoned

3,143

Zone 1 counties

1,069

Map drawn

1993

EPA action level

4.0 pCi/L

Your county's radon report

ZIP in, every county out, with the vintage and the caveat attached

About three ZIPs in ten touch more than one county, and the counties can sit in different zones, so the report shows every county the ZIP touches with its land area share.

The map itself

One map, three zones, drawn in 1993 and never revised

Everything on this page rests on a single federal dataset, so here is exactly what it is and when it is from, in EPA's words:

“The Map of Radon Zones was developed in 1993 to identify areas of the U.S. with the greatest potential for elevated indoor radon levels based on indoor radon measurement data, geology, aerial radioactivity, soil parameters, and foundation types.”

EPA, EPA Map of Radon Zones and Supplemental Information

“Zone 1 (red zones) Highest potential; average indoor radon levels may be greater than 4 pCi/L (picocuries per liter). Zone 2 (orange zones) Moderate potential; average indoor radon levels may be between 2 and 4 pCi/L. Zone 3 (yellow zones) Low potential; average indoor radon levels may be less than 2 pCi/L.”

EPA, Radon Zones Map (accessible text version)

The EPA Map of Radon Zones showing every US county colored red for Zone 1, orange for Zone 2 or yellow for Zone 3 — The EPA Map of Radon Zones, reproduced from EPA's own accessible map document. Red is Zone 1, orange Zone 2, yellow Zone 3. Note the fine print EPA prints on the map itself: homes with elevated radon have been found in all three zones. “EPA Map of Radon Zones (1993), from EPA's accessible map PDF” — U.S. Environmental Protection Agency — Public domain

The map's age is a fact we print next to every zone, because a thirty-plus-year-old prediction deserves to be read as one. What has NOT changed since 1993: the geology the zones were largely built from. What has: county lines (seven current counties postdate the map and inherit zones from their predecessors, flagged wherever they appear), the amount of actual test data (millions of tests since), and EPA's framing, which now leads with the caveat:

“The map should not be used to determine if a home in a given zone should be tested for radon. Homes with elevated levels of radon have been found in all three zones. All homes should be tested for radon.”

EPA, Radon Zones Map (accessible text version)

Our county assignments come from EPA's own map service, the one behind EPA's current interactive map, fetched 2026-09-02. We audited it against EPA's downloadable zone spreadsheet and found eight counties where EPA's two publications disagree. Six could be checked against EPA's published state map PDFs and the map service was right all six times; the last two, Ketchikan Gateway in Alaska and Somerset in Maryland, are clipped off the edge of their state PDFs, so this site shows both values for those two counties rather than picking one.

Summarised from EPA geodata radon zones map service in our own words.

State by state

All 50 states, ranked by share of Zone 1 counties

Iowa and North Dakota are the only states where every county is Zone 1. 12 states have no Zone 1 county at all (Alaska, Arizona, Arkansas, Delaware, Florida, Hawaii, Louisiana, Mississippi, Oklahoma, Oregon, Texas, Vermont), and EPA's testing advice is identical in all of them, which tells you how to read this table: as a map of where the odds run high, never as permission to skip the test.

State	Counties	Zone 1	Zone 2	Zone 3
Iowa	99	99	0	0
North Dakota	53	53	0	0
Wyoming	23	21	2	0
Montana	56	49	7	0
Colorado	64	52	12	0
Minnesota	87	68	19	0
Maine	16	12	4	0
Pennsylvania	67	49	17	1
South Dakota	66	48	18	0
Indiana	92	57	35	0
Kansas	105	65	40	0
Ohio	88	53	35	0
Nebraska	93	53	24	16
Illinois	102	56	43	3
New York	62	34	13	15
Nevada	17	9	7	1
Connecticut	8	4	3	1
Virginia	133	62	29	42
Idaho	44	19	20	5
Rhode Island	5	2	2	1
Tennessee	95	38	32	25
Wisconsin	72	28	44	0
West Virginia	55	20	29	6
Maryland	24	8	8	8
New Jersey	21	7	11	3
Kentucky	120	30	82	8
Utah	29	7	22	0
Massachusetts	14	3	10	1
New Mexico	33	7	26	0
Alabama	67	13	33	21
Washington	39	7	14	18
Michigan	83	9	32	42
New Hampshire	10	1	9	0
Missouri	115	11	97	7
North Carolina	100	8	31	61
California	58	2	29	27
Georgia	159	4	55	100
South Carolina	46	1	8	37
Alaska	30	0	5	25
Arizona	15	0	15	0
Arkansas	75	0	14	61
Delaware	3	0	1	2
Florida	67	0	9	58
Hawaii	5	0	0	5
Louisiana	64	0	0	64
Mississippi	82	0	8	74
Oklahoma	77	0	9	68
Oregon	36	0	21	15
Texas	254	0	39	215
Vermont	14	0	12	2

How to test

January is the season, and the test wants the windows shut

Radon testing has an actual season, and it is winter. January is National Radon Action Month on EPA's calendar, when most state programs run their free and discounted kit campaigns, and the physics cooperates: a short-term test wants closed-house conditions, which a heated house in January maintains without trying.

“Test your home - EPA and the U.S. Surgeon General recommend that all homes in the U.S. be tested for radon. Testing is easy and inexpensive.”

EPA, National Radon Action Month Information ("Five Things You Can Do During National Radon Action Month")

“Follow the instructions that come with your test kit. If you are doing a short-term test, close your windows and outside doors and keep them closed as much as possible during the test.”

EPA, A Citizen's Guide to Radon

A technician in a safety vest retrieving two dome shaped radon detectors mounted on a do not disturb card on a wall — Radon detectors being collected during a US Navy housing survey. The card says do not disturb because the device is averaging the air over days; moving it mid-test is the classic way to ruin one. “NSA Naples, Italy Radon Detector Collection (9333293)” — U.S. Navy photo — Public domain

What the numbers on a result mean is EPA's call, and EPA has published it plainly:

“The EPA recommends homes be fixed if the radon level is 4 pCi/L (picocuries per liter) (150 becquerels per meter cubed (Bq/m3)) or more. Because there is no known safe level of exposure to radon, the EPA also recommends that Americans consider fixing their home for radon levels between 2 pCi/L and 4 pCi/L (75 - 150 Bq/m3).”

EPA, What is EPA's Action Level for Radon and What Does it Mean?

“The average indoor radon concentration for America’s homes is about 1.3 pCi/L (50 Bq/m3). It is upon this national average indoor level that the EPA based its estimate of 21,000 radon-related lung cancers a year. The average concentration of radon in outdoor air is .4 pCi/L (15 Bq/m3) or 1/10th of EPA's 4 pCi/L (150 Bq/m3) action level.”

EPA, What is EPA's Action Level for Radon and What Does it Mean?

A consumer digital radon monitor on a wooden table showing a long term average of 17 and a short term average of 22 becquerels per cubic meter — A consumer continuous monitor reading in becquerels per cubic meter, the international unit; 37 Bq/m3 equals 1 pCi/L, so this display's long-term 17 Bq/m3 is about 0.46 pCi/L. Worth knowing before a European-market device alarms you or falsely reassures you. “Radon detector” by CKristiansen, CC BY-SA 4.0

Where radon gets in is the least mysterious part: soil gas moves through whatever openings the foundation offers, and a fix is a pipe and a fan that give it an easier way out. EPA's Citizen's Guide covers testing and its companion guide covers fixing; EPA's test kit and professional finder covers who to call. State programs keep the certified mitigator lists.

An open sump pit in a basement floor with a sump pump, float switch and discharge pipes visible — An open sump pit, one of the textbook radon entry routes: a hole in the slab connected directly to the soil. Mitigation systems often draw from exactly here, with a sealed lid and a fan turning the house's biggest leak into its exhaust point. “A newly-installed sump pump in the basement of a house in Ewing Township, New Jersey” by Famartin, CC BY-SA 4.0

What the agencies say

The health case, entirely in EPA's words

“Radon is the number one cause of lung cancer among non-smokers, according to EPA estimates. Overall, radon is the second leading cause of lung cancer. Radon is responsible for about 21,000 lung cancer deaths every year. About 2,900 of these deaths occur among people who have never smoked.”

EPA, Health Risk of Radon

“You can’t see, smell or taste radon, but it could be present at a dangerous level in your home. Radon is the leading cause of lung cancer deaths among nonsmokers in America and claims the lives of about 21,000 Americans each year.”

EPA, National Radon Action Month Information

The rest, including risk tables by smoking status, the BEIR VI report and the 2005 Surgeon General advisory, lives at EPA, Health Risk of Radon. This site adds nothing to it and subtracts nothing from it. Personal risk questions belong with your doctor.

Where this comes from

Where the data comes from

Zones. EPA Map of Radon Zones (EPA 402-R-93-071, 1993), county assignments from EPA's map service, cross-checked against EPA's zone spreadsheet and EPA's published state maps. A US Government work in the public domain. ZIP resolution. US Census Bureau 2020 ZCTA to county relationship file, committed to this site, with land area shares. Newer state data. New York State Department of Health county test results (updated 2025-11-18) and counts of the Pennsylvania DEP's posted results (through 2026-07-08), each dated where shown; other states' publications are linked from their pages. Zones describe counties; tests describe homes. Every page keeps those two apart, with no per-home estimate or verdict of its own.

Common questions

Radon zones FAQ

What is the EPA Map of Radon Zones?

EPA's own description: "The Map of Radon Zones was developed in 1993 to identify areas of the U.S. with the greatest potential for elevated indoor radon levels based on indoor radon measurement data, geology, aerial radioactivity, soil parameters, and foundation types." It assigns every US county to Zone 1 (highest potential), Zone 2 (moderate) or Zone 3 (low). It is a 1993 map, it has not been revised, and this site states that vintage next to every zone it shows.

Can the map tell me whether my home has radon?

What do Zone 1, Zone 2 and Zone 3 mean?

EPA's definitions, verbatim: "Zone 1 (red zones) Highest potential; average indoor radon levels may be greater than 4 pCi/L (picocuries per liter). Zone 2 (orange zones) Moderate potential; average indoor radon levels may be between 2 and 4 pCi/L. Zone 3 (yellow zones) Low potential; average indoor radon levels may be less than 2 pCi/L." The prediction is a county average indoor screening level, built in 1993 from measurement data, geology, aerial radioactivity, soil parameters and foundation types.

What radon level should make me act?

EPA's action level, quoted: "The EPA recommends homes be fixed if the radon level is 4 pCi/L (picocuries per liter) (150 becquerels per meter cubed (Bq/m3)) or more. Because there is no known safe level of exposure to radon, the EPA also recommends that Americans consider fixing their home for radon levels between 2 pCi/L and 4 pCi/L (75 - 150 Bq/m3)." Those are EPA's thresholds, and the only ones on this site.

Why does my ZIP code show more than one county?

When should I test?

Is radon actually dangerous?

EPA's assessment, verbatim: "Radon is the number one cause of lung cancer among non-smokers, according to EPA estimates. Overall, radon is the second leading cause of lung cancer. Radon is responsible for about 21,000 lung cancer deaths every year. About 2,900 of these deaths occur among people who have never smoked." Health questions belong with EPA, the Surgeon General's 2005 advisory, your state radon program and your doctor, and every page here links them.