Colorado Radon Levels
53Zone 1 (High)
11Zone 2 (Moderate)
0Zone 3 (Low)
83% of counties in Colorado 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 |
|---|---|---|
| Adams County | Zone 1 | Highest Potential |
| Alamosa County | Zone 2 | Moderate Potential |
| Arapahoe County | Zone 1 | Highest Potential |
| Archuleta County | Zone 2 | Moderate Potential |
| Baca County | Zone 1 | Highest Potential |
| Bent County | Zone 1 | Highest Potential |
| Boulder County | Zone 1 | Highest Potential |
| Broomfield County | Zone 1 | Highest Potential |
| Chaffee County | Zone 1 | Highest Potential |
| Cheyenne County | Zone 1 | Highest Potential |
| Clear Creek County | Zone 1 | Highest Potential |
| Conejos County | Zone 2 | Moderate Potential |
| Costilla County | Zone 2 | Moderate Potential |
| Crowley County | Zone 1 | Highest Potential |
| Custer County | Zone 1 | Highest Potential |
| Delta County | Zone 1 | Highest Potential |
| Denver County | Zone 1 | Highest Potential |
| Dolores County | Zone 1 | Highest Potential |
| Douglas County | Zone 1 | Highest Potential |
| Eagle County | Zone 2 | Moderate Potential |
| Elbert County | Zone 1 | Highest Potential |
| El Paso County | Zone 1 | Highest Potential |
| Fremont County | Zone 1 | Highest Potential |
| Garfield County | Zone 1 | Highest Potential |
| Gilpin County | Zone 1 | Highest Potential |
| Grand County | Zone 1 | Highest Potential |
| Gunnison County | Zone 1 | Highest Potential |
| Hinsdale County | Zone 2 | Moderate Potential |
| Huerfano County | Zone 1 | Highest Potential |
| Jackson County | Zone 1 | Highest Potential |
| Jefferson County | Zone 1 | Highest Potential |
| Kiowa County | Zone 1 | Highest Potential |
| Kit Carson County | Zone 1 | Highest Potential |
| Lake County | Zone 1 | Highest Potential |
| La Plata County | Zone 1 | Highest Potential |
| Larimer County | Zone 1 | Highest Potential |
| Las Animas County | Zone 1 | Highest Potential |
| Lincoln County | Zone 1 | Highest Potential |
| Logan County | Zone 1 | Highest Potential |
| Mesa County | Zone 1 | Highest Potential |
| Mineral County | Zone 2 | Moderate Potential |
| Moffat County | Zone 1 | Highest Potential |
| Montezuma County | Zone 1 | Highest Potential |
| Montrose County | Zone 1 | Highest Potential |
| Morgan County | Zone 1 | Highest Potential |
| Otero County | Zone 1 | Highest Potential |
| Ouray County | Zone 1 | Highest Potential |
| Park County | Zone 1 | Highest Potential |
| Phillips County | Zone 1 | Highest Potential |
| Pitkin County | Zone 1 | Highest Potential |
| Prowers County | Zone 1 | Highest Potential |
| Pueblo County | Zone 1 | Highest Potential |
| Rio Blanco County | Zone 1 | Highest Potential |
| Rio Grande County | Zone 2 | Moderate Potential |
| Routt County | Zone 2 | Moderate Potential |
| Saguache County | Zone 2 | Moderate Potential |
| San Juan County | Zone 2 | Moderate Potential |
| San Miguel County | Zone 1 | Highest Potential |
| Sedgwick County | Zone 1 | Highest Potential |
| Summit County | Zone 1 | Highest Potential |
| Teller County | Zone 1 | Highest Potential |
| Washington County | Zone 1 | Highest Potential |
| Weld County | Zone 1 | Highest Potential |
| Yuma County | Zone 1 | Highest Potential |