Radon
Radon zones by state and county
Radon is a radioactive gas that seeps from soil and rock into homes. It has no smell or color, and EPA ranks it as the second leading cause of lung cancer after smoking. EPA's radon map places every county in one of three zones by predicted indoor level.
Radon guides
How to test your home for radonKits, placement and how long to leave themWhat is a safe radon level?Read your result against EPA's numbersRadon mitigation costWhat official sources say and what drives a quoteHow a radon mitigation system worksSuction pipe, fan and the methods behind themRadon health risksLung cancer risk by level, smokers and non-smokersRadon when buying or selling a homeTesting options during a sale and what to ask
Find your county's zone
What the zones mean
| Zone | Predicted average indoor level | Counties |
|---|---|---|
| Zone 1 | Above 4 pCi/L, EPA's action level | 1,073 |
| Zone 2 | 2 to 4 pCi/L | 1,027 |
| Zone 3 | Below 2 pCi/L | 1,026 |
Homes with high radon have been found in all three zones. The map guides where to focus programs; it does not tell you your home's level. Only a test does.
States by share of residents in Zone 1 counties
| State | Zone 1 counties | Residents in Zone 1 counties |
|---|---|---|
| Iowa | 99 of 99 | 100% |
| Colorado | 53 of 64 | 98% |
| Minnesota | 68 of 87 | 81% |
| Pennsylvania | 49 of 67 | 77% |
| Ohio | 53 of 88 | 63% |
| Illinois | 56 of 102 | 27% |
| Idaho | 19 of 44 | 24% |
| New Jersey | 7 of 21 | 24% |
| New York | 34 of 62 | 23% |
| Michigan | 9 of 83 | 12% |
| Utah | 7 of 29 | 4% |
| California | 2 of 58 | 3% |
| Arizona | 0 of 15 | 0% |
| Florida | 0 of 67 | 0% |
| Texas | 0 of 254 | 0% |
Sources: EPA Map of Radon Zones (county list, 2024 file); US Census Bureau 2024 county population estimates. Updated October 2026.