Idaho: 44 counties covered
Of 44 rated Idaho counties, 19 are in EPA's highest radon-potential zone (Zone 1) — but every county page links to testing guidance regardless of zone, because a county rating is a county-wide average, not a reading for any one house.
- Ada County
- Canyon County
- Kootenai County
- Bonneville County
- Twin Falls County
- Bannock County
- Madison County
- Bonner County
- Bingham County
- Nez Perce County
- Latah County
- Jefferson County
- Elmore County
- Payette County
- Jerome County
- Cassia County
- Blaine County
- Minidoka County
- Gem County
- Idaho County
- Gooding County
- Franklin County
- Fremont County
- Shoshone County
- Boundary County
- Teton County
- Valley County
- Owyhee County
- Washington County
- Benewah County
- Clearwater County
- Boise County
- Lemhi County
- Power County
- Caribou County
- Bear Lake County
- Lincoln County
- Adams County
- Oneida County
- Custer County
- Lewis County
- Butte County
- Camas County
- Clark County