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Radon map: radon levels by county and ZIP code

EPA's Map of Radon Zones places 1,070 of the 3,144 US counties in Zone 1, where the predicted average indoor radon screening level is above 4 pCi/L, 1,031 in Zone 2 and 1,036 in Zone 3. Radon testing laboratories reported 1,408,802 building tests nationally for 2008 to 2017; 36.5% were at or above EPA's 4 pCi/L action level. Look up any county, ZIP code or address below.

EPA map of radon zones by state

ALAKAZARCACOCTDEDCFLGAHIIDILINIAKSKYLAMEMDMAMIMNMSMOMTNENVNHNJNMNYNCNDOHOKORPARISCSDTNTXUTVTVAWAWVWIWY
Share of each state's counties in EPA radon Zone 1:75% or more50 to 74%25 to 49%under 25%none

EPA developed the Map of Radon Zones 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”. Every county gets one of three zones. EPA adds: “This map should not be used to determine if individual homes need to be tested.”

Radon zones and test results by state

Counties per EPA radon zone and laboratory radon test results, by state
StateZone 1Zone 2Zone 3Lab tests 2008-20174 pCi/L or more
Alabama1333218,14821.3%
Alaska0524 +168017.3%
Arizona01502,22916.8%
Arkansas0146145022.9%
California229275,66310.7%
Colorado5311069,62046.6%
Connecticut300 +60n/a
Delaware01210,73516.8%
Washington, DC0011,5788.7%
Florida095846,24123.1%
Georgia45510024,06324.5%
Hawaii0050n/a
Idaho192059,53140.3%
Illinois5643385,53243.2%
Indiana5735036,72538.6%
Iowa990068,66357.1%
Kansas654000n/a
Kentucky3082820,87042.8%
Louisiana00642032.9%
Maine12408,78838.5%
Maryland89735,20124.2%
Massachusetts310195,40923.6%
Michigan9324282,44926.3%
Minnesota6819090,82642.8%
Mississippi08740n/a
Missouri1197742,91330.7%
Montana49706,61245.6%
Nebraska53241629,75857.9%
Nevada9718,48322.4%
New Hampshire19010,47134.9%
New Jersey71130n/a
New Mexico72602,63728.8%
New York34131565,89324.2%
North Carolina8316143,94522.5%
North Dakota53005,05458.9%
Ohio5335084,32551.6%
Oklahoma096850112.5%
Oregon0211517,03425.2%
Pennsylvania49171173,28441.1%
Rhode Island22125,84523.7%
South Carolina183715,85518.1%
South Dakota481804,76058.6%
Tennessee39322423,07132.8%
Texas0392152,38211.3%
Utah722021,45041.9%
Vermont01227,20022.3%
Virginia62284340,38830.8%
Washington714185,87925.3%
West Virginia202967,38638%
Wisconsin2844055,35947%
Wyoming21204,71343.1%

Zone counts are counties (and county equivalents); “+” marks counties without a single zone (Connecticut planning regions whose towns span zones, and one Alaska census area). Lab tests and the share at or above 4 pCi/L are computed from county counts and percents for 2008 to 2017; counties with too few tests to report are not included.

States with the highest radon test results

The share of laboratory tests at or above EPA's 4 pCi/L action level, 2008 to 2017, for states with at least 1,000 tests. Test results come from buildings whose owners chose to test, so they describe the tests on file rather than every home.

  1. 1.North Dakota: 58.9% of 5,054 tests
  2. 2.South Dakota: 58.6% of 4,760 tests
  3. 3.Nebraska: 57.9% of 29,758 tests
  4. 4.Iowa: 57.1% of 68,663 tests
  5. 5.Ohio: 51.6% of 84,325 tests
  6. 6.Wisconsin: 47% of 55,359 tests
  7. 7.Colorado: 46.6% of 69,620 tests
  8. 8.Montana: 45.6% of 6,612 tests
  9. 9.Illinois: 43.2% of 85,532 tests
  10. 10.Wyoming: 43.1% of 4,713 tests

Radon levels by ZIP code

No record measures radon in every ZIP code. The lookup above turns a ZIP code into the county or counties it covers (by land area) and shows each county's zone and test results. Pennsylvania is the exception: its state records include every radon test reported since 1986 with the ZIP code, 3,334,280 results through 2026-07, so Pennsylvania ZIP codes with 10 or more tests show their own median and share at or above 4 pCi/L. New York's state records are by town, shown on each New York county page.

Why the 4 pCi/L action level matters

EPA says to fix a home “if your radon level is 4 picocuries per liter (pCi/L) (150 becquerels per cubic meter (Bq/m3)) or higher” and to consider fixing it between 2 and 4 pCi/L. By EPA's estimates radon is the number one cause of lung cancer among non-smokers and the second leading cause overall, responsible for about 21,000 lung cancer deaths every year, about 2,900 of them among people who never smoked.

Buying a home? A radon reading belongs to the building, not the county, so the county numbers here are a reason to test, not a substitute for it. The Environmental Records Report lists the county's zone and test results with the flood zone, mapped faults, power lines and federal contamination records near the address. For ownership, deeds, mortgages and liens, a title report is $49 per report in the counties we cover.

Radon, flood, faults and contamination for one address

Environmental Records Report, $29. PDF and JSON, usually ready in about a minute.

Radon map questions

What is the EPA radon map?

EPA's Map of Radon Zones was developed in 1993 to identify areas with the greatest potential for elevated indoor radon, from indoor measurements, geology, aerial radioactivity, soil and foundation types. It puts every county in Zone 1 (predicted average indoor screening level above 4 pCi/L), Zone 2 (2 to 4 pCi/L) or Zone 3 (below 2 pCi/L). Of today's 3,144 counties, 1,070 are in Zone 1, 1,031 in Zone 2 and 1,036 in Zone 3. EPA says: "This map should not be used to determine if individual homes need to be tested."

How do I find radon levels by ZIP code?

Enter the ZIP code in the lookup on this page. It finds the county (or counties) the ZIP code covers, by land area, and shows each county's EPA zone and the radon test results on file. In Pennsylvania it also shows the state's results for the ZIP code itself. No record measures every home in a ZIP code; only a test of the building gives its level.

Which states have the highest radon levels?

By radon laboratory test data for 2008 to 2017 (states with at least 1,000 tests), the highest shares of tests at or above 4 pCi/L were in North Dakota (58.9% of 5,054 tests), South Dakota (58.6% of 4,760 tests), Nebraska (57.9% of 29,758 tests), Iowa (57.1% of 68,663 tests), Ohio (51.6% of 84,325 tests). Across all counties with data, 36.5% of 1,408,802 tests were at or above 4 pCi/L. Tested buildings are self-selected, so these shares describe the tests, not every home.

What radon level is safe?

EPA says there is no known safe level of exposure to radon. It recommends fixing a home at 4 picocuries per liter (pCi/L) or more, and considering a fix between 2 and 4 pCi/L. The average indoor level in US homes is about 1.3 pCi/L and outdoor air averages about 0.4 pCi/L. EPA estimates radon causes about 21,000 lung cancer deaths a year and is the number one cause of lung cancer among non-smokers.

Does a Zone 3 county mean my house has low radon?

No. The zone is a county-wide prediction from 1993. In national laboratory data, 36.5% of tests nationally were at or above 4 pCi/L, and Zone 3 counties have homes above the action level too. EPA's advice is the same in every zone: test the home.

How do I know the radon level in my house?

Only by testing the building. EPA's advice is to test your home no matter where you live, and it calls testing easy and inexpensive. EPA's radon program materials point to every state's radon program, which is the place to ask about test kits and testers. County zones and test results, like the ones on this site, only say how common high readings are nearby.

Other free hazard lookups

All of these, plus wetlands, FEMA hazard ratings and the federal contamination lists, are in the Environmental Records Report for any US address ($29).

Data compiled 2026-10-20. County-level screening information from official records, not a radon measurement of any building and not medical or professional advice. Every state page lists its counties; every county page lists its own numbers.

Order a title search: owner of record, deeds, mortgages and liens, $49 per report.