EPA Map of Radon Zones
Radon zones, county by county
Radon is a radioactive gas produced by uranium decaying in soil and rock. It has no colour, no smell and no taste, it seeps into buildings through the foundation, and the EPA attributes about 21,000 lung cancer deaths a year in the United States to it. That makes it the second leading cause of lung cancer overall and the leading cause among people who have never smoked.
The EPA assigns each of the 3,143 US counties to one of three zones based on the indoor radon level it predicts for that county. The zone is a prediction about the ground, not a measurement of any building. Homes above the action level are found in every zone, which is why the recommendation to test does not change with the zone.
The national picture
Where the ground produces radon
Shaded by the share of each state’s counties in Zone 1. The band running from the Great Plains through the upper Midwest and into the Appalachians is where uranium-bearing bedrock and glacial till meet basements, and it is visible from orbit as far as this map is concerned.
Hover a state for its Zone 1 count · click to open it
Find your county
Radon zones by state
Ranked by the share of counties in Zone 1. Iowa is the only state where every single county falls in the highest category.
| State | Counties | Zone 1 | Zone 2 | Zone 3 | Share in Zone 1 |
|---|---|---|---|---|---|
| Iowa | 99 | 99 | 0 | 0 | 100% |
| North Dakota | 53 | 53 | 0 | 0 | 100% |
| Wyoming | 23 | 21 | 2 | 0 | 91% |
| Montana | 56 | 49 | 7 | 0 | 88% |
| Colorado | 64 | 53 | 11 | 0 | 83% |
| Minnesota | 87 | 68 | 19 | 0 | 78% |
| Maine | 16 | 12 | 4 | 0 | 75% |
| Pennsylvania | 67 | 49 | 17 | 1 | 73% |
| South Dakota | 66 | 48 | 18 | 0 | 73% |
| Indiana | 92 | 57 | 35 | 0 | 62% |
| Kansas | 105 | 65 | 40 | 0 | 62% |
| Ohio | 88 | 53 | 35 | 0 | 60% |
| Nebraska | 93 | 53 | 24 | 16 | 57% |
| Illinois | 102 | 56 | 43 | 3 | 55% |
| New York | 62 | 34 | 13 | 15 | 55% |
| Nevada | 17 | 9 | 7 | 1 | 53% |
| Connecticut | 8 | 4 | 3 | 1 | 50% |
| Virginia | 133 | 62 | 28 | 43 | 47% |
| Idaho | 44 | 19 | 20 | 5 | 43% |
| Tennessee | 95 | 39 | 32 | 24 | 41% |
| Rhode Island | 5 | 2 | 2 | 1 | 40% |
| Wisconsin | 72 | 28 | 44 | 0 | 39% |
| West Virginia | 55 | 20 | 29 | 6 | 36% |
| Maryland | 24 | 8 | 9 | 7 | 33% |
| New Jersey | 21 | 7 | 11 | 3 | 33% |
| Kentucky | 120 | 30 | 82 | 8 | 25% |
| Utah | 29 | 7 | 22 | 0 | 24% |
| Massachusetts | 14 | 3 | 10 | 1 | 21% |
| New Mexico | 33 | 7 | 26 | 0 | 21% |
| Alabama | 67 | 13 | 33 | 21 | 19% |
| Washington | 39 | 7 | 14 | 18 | 18% |
| Michigan | 83 | 9 | 32 | 42 | 11% |
| New Hampshire | 10 | 1 | 9 | 0 | 10% |
| Missouri | 115 | 11 | 97 | 7 | 10% |
| North Carolina | 100 | 8 | 31 | 61 | 8% |
| California | 58 | 2 | 29 | 27 | 3% |
| Georgia | 159 | 4 | 55 | 100 | 3% |
| South Carolina | 46 | 1 | 8 | 37 | 2% |
| Alaska | 30 | 0 | 5 | 25 | 0% |
| Arizona | 15 | 0 | 15 | 0 | 0% |
| Arkansas | 75 | 0 | 14 | 61 | 0% |
| Delaware | 3 | 0 | 1 | 2 | 0% |
| District of Columbia | 1 | 0 | 0 | 1 | 0% |
| Florida | 67 | 0 | 9 | 58 | 0% |
| Hawaii | 5 | 0 | 0 | 5 | 0% |
| Louisiana | 64 | 0 | 0 | 64 | 0% |
| Mississippi | 82 | 0 | 8 | 74 | 0% |
| Oklahoma | 77 | 0 | 9 | 68 | 0% |
| Oregon | 36 | 0 | 21 | 15 | 0% |
| Texas | 254 | 0 | 39 | 215 | 0% |
| Vermont | 14 | 0 | 12 | 2 | 0% |
EPA Map of Radon Zones, current release. The map was built from indoor radon measurements, geology, aerial radioactivity, soil parameters and foundation types. It was designed to help target resources, and the EPA is explicit that it should not be used to decide whether an individual home needs testing.
Understanding the map
What a zone does and does not tell you
What it tells you
- The average indoor radon screening level the EPA predicts across the county.
- How urgently a state or county programme should be pushing testing locally.
- Whether new construction in the area is a candidate for radon-resistant features.
What it does not
- Predict the level in any particular house. Two neighbouring homes routinely differ by more than the gap between zones.
- Mean a Zone 3 home is safe. Homes above 4 pCi/L are found in all three zones.
- Replace a test. The EPA recommends testing every home regardless of zone.
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