Colorado: 64 counties covered
Of 64 rated Colorado counties, 52 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.
- El Paso County
- Denver County
- Arapahoe County
- Jefferson County
- Adams County
- Douglas County
- Larimer County
- Weld County
- Boulder County
- Pueblo County
- Mesa County
- Broomfield County
- Garfield County
- La Plata County
- Eagle County
- Fremont County
- Montrose County
- Delta County
- Summit County
- Morgan County
- Elbert County
- Montezuma County
- Routt County
- Teller County
- Chaffee County
- Logan County
- Park County
- Otero County
- Gunnison County
- Alamosa County
- Pitkin County
- Grand County
- Las Animas County
- Archuleta County
- Moffat County
- Prowers County
- Rio Grande County
- Yuma County
- Clear Creek County
- San Miguel County
- Conejos County
- Lake County
- Kit Carson County
- Huerfano County
- Saguache County
- Rio Blanco County
- Gilpin County
- Bent County
- Crowley County
- Lincoln County
- Custer County
- Ouray County
- Washington County
- Phillips County
- Costilla County
- Baca County
- Dolores County
- Sedgwick County
- Cheyenne County
- Kiowa County
- Jackson County
- Mineral County
- San Juan County
- Hinsdale County