Idaho Radon Levels
19Zone 1 (High)
20Zone 2 (Moderate)
5Zone 3 (Low)
43% of counties in Idaho are classified as EPA Zone 1 (highest radon potential), meaning predicted average indoor radon levels exceed 4 pCi/L — the EPA action level. The EPA recommends that all homes be tested for radon, regardless of zone classification.
| County | EPA Zone | Risk Level |
|---|---|---|
| Ada County | Zone 2 | Moderate Potential |
| Adams County | Zone 3 | Lowest Potential |
| Bannock County | Zone 2 | Moderate Potential |
| Bear Lake County | Zone 2 | Moderate Potential |
| Benewah County | Zone 1 | Highest Potential |
| Bingham County | Zone 2 | Moderate Potential |
| Blaine County | Zone 1 | Highest Potential |
| Boise County | Zone 1 | Highest Potential |
| Bonner County | Zone 1 | Highest Potential |
| Bonneville County | Zone 2 | Moderate Potential |
| Boundary County | Zone 1 | Highest Potential |
| Butte County | Zone 1 | Highest Potential |
| Camas County | Zone 1 | Highest Potential |
| Canyon County | Zone 2 | Moderate Potential |
| Caribou County | Zone 2 | Moderate Potential |
| Cassia County | Zone 2 | Moderate Potential |
| Clark County | Zone 1 | Highest Potential |
| Clearwater County | Zone 1 | Highest Potential |
| Custer County | Zone 1 | Highest Potential |
| Elmore County | Zone 1 | Highest Potential |
| Franklin County | Zone 2 | Moderate Potential |
| Fremont County | Zone 1 | Highest Potential |
| Gem County | Zone 3 | Lowest Potential |
| Gooding County | Zone 1 | Highest Potential |
| Idaho County | Zone 1 | Highest Potential |
| Jefferson County | Zone 2 | Moderate Potential |
| Jerome County | Zone 2 | Moderate Potential |
| Kootenai County | Zone 1 | Highest Potential |
| Latah County | Zone 1 | Highest Potential |
| Lemhi County | Zone 1 | Highest Potential |
| Lewis County | Zone 3 | Lowest Potential |
| Lincoln County | Zone 2 | Moderate Potential |
| Madison County | Zone 2 | Moderate Potential |
| Minidoka County | Zone 2 | Moderate Potential |
| Nez Perce County | Zone 3 | Lowest Potential |
| Oneida County | Zone 2 | Moderate Potential |
| Owyhee County | Zone 2 | Moderate Potential |
| Payette County | Zone 2 | Moderate Potential |
| Power County | Zone 2 | Moderate Potential |
| Shoshone County | Zone 1 | Highest Potential |
| Teton County | Zone 2 | Moderate Potential |
| Twin Falls County | Zone 2 | Moderate Potential |
| Valley County | Zone 1 | Highest Potential |
| Washington County | Zone 3 | Lowest Potential |