Radon and home risks by county
Radon in Idaho
19 of Idaho's 44 counties are in EPA's highest radon zone, home to about 24% of the state's residents. Radon zones describe an area's potential; EPA recommends testing every home regardless of zone.
Zone 1 counties
19
high radon potential
Zone 2 counties
20
moderate potential
Zone 3 counties
5
low potential
Counties with water violations
38
since 2016; 7 with unresolved ones
Find your county by ZIP
Zone 1: high potential (19 counties)
| County | Residents | Water systems | Health violations since 2016 | Unresolved |
|---|---|---|---|---|
| Benewah County | 10,529 | 9 | 1 | 0 |
| Blaine County | 25,261 | 22 | 16 | 0 |
| Boise County | 8,581 | 20 | 42 | 0 |
| Bonner County | 53,955 | 53 | 13 | 0 |
| Boundary County | 14,040 | 14 | 74 | 2 |
| Butte County | 2,735 | 4 | 1 | 0 |
| Camas County | 1,247 | 1 | 0 | 0 |
| Clark County | 794 | 1 | 0 | 0 |
| Clearwater County | 9,151 | 11 | 10 | 0 |
| Custer County | 4,597 | 4 | 0 | 0 |
| Elmore County | 29,729 | 24 | 34 | 0 |
| Fremont County | 14,399 | 11 | 14 | 5 |
| Gooding County | 16,189 | 8 | 2 | 2 |
| Idaho County | 17,912 | 18 | 61 | 0 |
| Kootenai County | 188,323 | 115 | 6 | 2 |
| Latah County | 42,180 | 21 | 12 | 0 |
| Lemhi County | 8,397 | 5 | 15 | 0 |
| Shoshone County | 14,074 | 15 | 1 | 0 |
| Valley County | 12,777 | 12 | 7 | 0 |
Zone 2: moderate potential (20 counties)
| County | Residents | Water systems | Health violations since 2016 | Unresolved |
|---|---|---|---|---|
| Ada County | 535,799 | 53 | 7 | 0 |
| Bannock County | 91,010 | 23 | 1 | 0 |
| Bear Lake County | 6,779 | 12 | 2 | 0 |
| Bingham County | 50,889 | 28 | 5 | 0 |
| Bonneville County | 133,644 | 35 | 15 | 1 |
| Canyon County | 266,892 | 84 | 24 | 0 |
| Caribou County | 7,239 | 8 | 1 | 0 |
| Cassia County | 25,976 | 13 | 11 | 0 |
| Franklin County | 15,638 | 15 | 4 | 1 |
| Jefferson County | 34,854 | 17 | 1 | 0 |
| Jerome County | 26,056 | 6 | 1 | 0 |
| Lincoln County | 5,556 | 4 | 7 | 0 |
| Madison County | 55,549 | 7 | 17 | 0 |
| Minidoka County | 22,691 | 9 | 11 | 0 |
| Oneida County | 4,976 | 1 | 0 | 0 |
| Owyhee County | 12,748 | 8 | 3 | 0 |
| Payette County | 27,662 | 7 | 10 | 0 |
| Power County | 8,381 | 5 | 9 | 0 |
| Teton County | 12,932 | 13 | 2 | 0 |
| Twin Falls County | 96,509 | 14 | 11 | 0 |
Zone 3: low potential (5 counties)
| County | Residents | Water systems | Health violations since 2016 | Unresolved |
|---|---|---|---|---|
| Adams County | 4,998 | 5 | 1 | 0 |
| Gem County | 21,857 | 6 | 0 | 0 |
| Lewis County | 3,728 | 6 | 5 | 1 |
| Nez Perce County | 42,847 | 12 | 4 | 0 |
| Washington County | 11,539 | 3 | 0 | 0 |
How to read this table
Water systems counts community systems that list the county in their service area; one system can serve several counties. Health violations are breaches of a legal limit or treatment rule recorded by EPA since January 2016, not paperwork lapses. A violation stays unresolved until the state records it as fixed.
Other states
- Arizona
- California
- Colorado
- Florida
- Illinois
- Iowa
- Michigan
- Minnesota
- New Jersey
- New York
- Ohio
- Pennsylvania
- Texas
- Utah
Sources: EPA Map of Radon Zones, EPA ECHO Safe Drinking Water Act data (2026Q3, published October 2026), US Census Bureau Vintage 2024 estimates. See the methodology.