Radon in Idaho
About 4 in 10 homes tested in Idaho were at or above the EPA action level of 4 pCi/L.
- Below 2 pCi/L: 32%
- 2 to 4 pCi/L: 27%
- 4 pCi/L or more: 40%
The EPA puts 19 of Idaho's 44 counties in Zone 1, its highest radon category, 20 in Zone 2 and 5 in Zone 3.
Every county in Idaho
Sorted by the share of homes tested at or above 4 pCi/L. Select a county for local details and costs.
| County | Homes tested | At or above 4 | Median | EPA zone |
|---|---|---|---|---|
| Bear Lake County | 78% | 7.8 pCi/L | 2 | |
| Butte County | 19 tests | – | – | 1 |
| Clark County | 1 tests | – | – | 1 |
| Oneida County | 74% | 6.5 pCi/L | 2 | |
| Custer County | 19 tests | – | – | 1 |
| Jefferson County | 67% | 5.7 pCi/L | 2 | |
| Lemhi County | 65% | 5.2 pCi/L | 1 | |
| Madison County | 64% | 6.2 pCi/L | 2 | |
| Shoshone County | 63% | 5.7 pCi/L | 1 | |
| Kootenai County | 61% | 6.0 pCi/L | 1 | |
| Cassia County | 60% | 5.4 pCi/L | 2 | |
| Blaine County | 58% | 5.3 pCi/L | 1 | |
| Teton County | 53% | 4.4 pCi/L | 2 | |
| Bingham County | 52% | 4.2 pCi/L | 2 | |
| Adams County | 18 tests | – | – | 3 |
| Lewis County | 6 tests | – | – | 3 |
| Fremont County | 50% | 3.9 pCi/L | 1 | |
| Elmore County | 48% | 3.8 pCi/L | 1 | |
| Caribou County | 44% | 3.4 pCi/L | 2 | |
| Bannock County | 42% | 3.2 pCi/L | 2 | |
| Bonneville County | 40% | 3.4 pCi/L | 2 | |
| Idaho County | 40% | 2.9 pCi/L | 1 | |
| Lincoln County | 15 tests | – | – | 2 |
| Franklin County | 35% | 3.1 pCi/L | 2 | |
| Bonner County | 33% | 2.3 pCi/L | 1 | |
| Benewah County | 31% | 2.4 pCi/L | 1 | |
| Clearwater County | 30% | 1.8 pCi/L | 1 | |
| Gooding County | 28% | 2.4 pCi/L | 1 | |
| Camas County | 2 tests | – | – | 1 |
| Valley County | 27% | 2.3 pCi/L | 1 | |
| Power County | 27% | 2.5 pCi/L | 2 | |
| Latah County | 26% | 1.7 pCi/L | 1 | |
| Ada County | 25% | 2.4 pCi/L | 2 | |
| Twin Falls County | 24% | 2.4 pCi/L | 2 | |
| Owyhee County | 23% | 2.1 pCi/L | 2 | |
| Boise County | 22% | 2.0 pCi/L | 1 | |
| Nez Perce County | 22% | 2.3 pCi/L | 3 | |
| Washington County | 21% | 2.1 pCi/L | 3 | |
| Gem County | 20% | 1.9 pCi/L | 3 | |
| Boundary County | 20% | 2.1 pCi/L | 1 | |
| Jerome County | 17% | 1.9 pCi/L | 2 | |
| Minidoka County | 15% | 1.8 pCi/L | 2 | |
| Canyon County | 11% | 1.6 pCi/L | 2 | |
| Payette County | 5% | 1.5 pCi/L | 2 |
"–" means fewer than 20 tests or no lab data, too few for a reliable figure.
Sources
- EPA Map of Radon Zones (public domain).
- CDC Environmental Public Health Tracking Network, radon tests from labs, 2008–2017. Pre-mitigation tests only.
Last updated October 2026. How we calculate these numbers.