EPA Map of Radon Zones
EPA radon zones by state
EPA puts 1,074 of 3,143 U.S. counties in Zone 1, its highest radon potential. In Iowa and North Dakota, every county is Zone 1.
From EPA's county list, checked October 1, 2026. EPA drew the map in 1993 and says not to use it to decide whether to test. Homes with high levels turn up in every zone.
What the zones mean
- Zone 1, highest potential: average indoor levels may be greater than 4 pCi/L.
- Zone 2, moderate potential: may be between 2 and 4 pCi/L.
- Zone 3, low potential: may be less than 2 pCi/L.
Wording from EPA's Map of Radon Zones page. EPA says to fix at 4 pCi/L or higher and consider fixing between 2 and 4.
Every state
| State | Counties in Zone 1 | Share |
|---|---|---|
| Iowa | 99 of 99 | 100% |
| North Dakota | 53 of 53 | 100% |
| Wyoming | 21 of 23 | 91% |
| Montana | 50 of 57 | 88% |
| Colorado | 53 of 64 | 83% |
| Minnesota | 68 of 87 | 78% |
| Maine | 12 of 16 | 75% |
| Pennsylvania | 49 of 67 | 73% |
| South Dakota | 48 of 66 | 73% |
| Indiana | 57 of 92 | 62% |
| Kansas | 65 of 105 | 62% |
| Ohio | 53 of 88 | 60% |
| Nebraska | 53 of 93 | 57% |
| Illinois | 56 of 102 | 55% |
| New York | 34 of 62 | 55% |
| Nevada | 9 of 17 | 53% |
| Connecticut | 4 of 8 | 50% |
| Virginia | 64 of 136 | 47% |
| Idaho | 19 of 44 | 43% |
| Tennessee | 39 of 95 | 41% |
| Rhode Island | 2 of 5 | 40% |
| Wisconsin | 28 of 72 | 39% |
| West Virginia | 20 of 55 | 36% |
| Maryland | 8 of 24 | 33% |
| New Jersey | 7 of 21 | 33% |
| Kentucky | 30 of 120 | 25% |
| Utah | 7 of 29 | 24% |
| Massachusetts | 3 of 14 | 21% |
| New Mexico | 7 of 33 | 21% |
| Alabama | 13 of 67 | 19% |
| Washington | 7 of 39 | 18% |
| Michigan | 9 of 83 | 11% |
| New Hampshire | 1 of 10 | 10% |
| Missouri | 11 of 115 | 10% |
| North Carolina | 8 of 100 | 8% |
| California | 2 of 58 | 3% |
| Georgia | 4 of 159 | 3% |
| South Carolina | 1 of 46 | 2% |
| Alaska | 0 of 27 | 0% |
| Arizona | 0 of 15 | 0% |
| Arkansas | 0 of 75 | 0% |
| Delaware | 0 of 3 | 0% |
| Florida | 0 of 67 | 0% |
| Hawaii | 0 of 5 | 0% |
| Louisiana | 0 of 64 | 0% |
| Mississippi | 0 of 82 | 0% |
| Oklahoma | 0 of 77 | 0% |
| Oregon | 0 of 36 | 0% |
| Texas | 0 of 254 | 0% |
| Vermont | 0 of 14 | 0% |
Source: EPA county radon zone list, which also gives each county's Zone 2 and Zone 3 status. The District of Columbia is not in the list.
Radon by the numbers
21,000
34%
Any home can be high or low, whatever the numbers say. A test is the only way to know yours. Checked October 1, 2026.
Next steps
Find a kit near you. Radon rules in your state. What your result means.