Radon and home risks by county
Radon in Colorado
53 of Colorado's 64 counties are in EPA's highest radon zone, home to about 98% of the state's residents. Radon zones describe an area's potential; EPA recommends testing every home regardless of zone.
Zone 1 counties
53
high radon potential
Zone 2 counties
11
moderate potential
Zone 3 counties
0
low potential
Counties with water violations
54
since 2016; 10 with unresolved ones
Find your county by ZIP
Zone 1: high potential (53 counties)
| County | Residents | Water systems | Health violations since 2016 | Unresolved |
|---|---|---|---|---|
| Adams County | 542,973 | 64 | 23 | 0 |
| Arapahoe County | 666,918 | 30 | 6 | 0 |
| Baca County | 3,367 | 6 | 44 | 0 |
| Bent County | 5,779 | 4 | 20 | 1 |
| Boulder County | 330,262 | 41 | 32 | 0 |
| Broomfield County | 78,323 | 3 | 0 | 0 |
| Chaffee County | 20,780 | 18 | 1 | 0 |
| Cheyenne County | 1,712 | 3 | 5 | 0 |
| Clear Creek County | 9,076 | 11 | 45 | 0 |
| Crowley County | 5,600 | 7 | 1 | 0 |
| Custer County | 5,553 | 3 | 0 | 0 |
| Delta County | 32,215 | 30 | 42 | 0 |
| Denver County | 729,019 | 5 | 0 | 0 |
| Dolores County | 2,467 | 2 | 6 | 0 |
| Douglas County | 393,995 | 29 | 33 | 0 |
| El Paso County | 752,772 | 74 | 66 | 2 |
| Elbert County | 29,382 | 15 | 6 | 0 |
| Fremont County | 50,093 | 16 | 0 | 0 |
| Garfield County | 63,167 | 55 | 20 | 0 |
| Gilpin County | 5,963 | 2 | 0 | 0 |
| Grand County | 16,154 | 24 | 7 | 0 |
| Gunnison County | 17,310 | 20 | 1 | 0 |
| Huerfano County | 6,988 | 10 | 30 | 1 |
| Jackson County | 1,273 | 2 | 0 | 0 |
| Jefferson County | 578,533 | 47 | 30 | 0 |
| Kiowa County | 1,392 | 3 | 19 | 0 |
| Kit Carson County | 7,080 | 6 | 49 | 1 |
| La Plata County | 56,823 | 54 | 56 | 0 |
| Lake County | 7,369 | 7 | 1 | 0 |
| Larimer County | 374,574 | 47 | 76 | 3 |
| Las Animas County | 14,518 | 14 | 4 | 0 |
| Lincoln County | 5,598 | 6 | 12 | 0 |
| Logan County | 20,755 | 9 | 25 | 0 |
| Mesa County | 161,260 | 21 | 3 | 0 |
| Moffat County | 13,142 | 6 | 2 | 0 |
| Montezuma County | 26,841 | 10 | 1 | 0 |
| Montrose County | 44,806 | 22 | 36 | 0 |
| Morgan County | 30,300 | 8 | 4 | 0 |
| Otero County | 17,991 | 23 | 632 | 4 |
| Ouray County | 5,197 | 5 | 5 | 0 |
| Park County | 18,316 | 11 | 6 | 3 |
| Phillips County | 4,488 | 3 | 2 | 0 |
| Pitkin County | 16,643 | 27 | 25 | 0 |
| Prowers County | 11,957 | 10 | 359 | 0 |
| Pueblo County | 169,866 | 18 | 99 | 2 |
| Rio Blanco County | 6,607 | 5 | 0 | 0 |
| San Miguel County | 7,819 | 12 | 36 | 0 |
| Sedgwick County | 2,257 | 3 | 1 | 0 |
| Summit County | 30,882 | 24 | 6 | 0 |
| Teller County | 24,862 | 24 | 77 | 3 |
| Washington County | 4,771 | 2 | 2 | 0 |
| Weld County | 369,745 | 58 | 23 | 0 |
| Yuma County | 10,048 | 4 | 5 | 0 |
Zone 2: moderate potential (11 counties)
| County | Residents | Water systems | Health violations since 2016 | Unresolved |
|---|---|---|---|---|
| Alamosa County | 16,689 | 4 | 29 | 0 |
| Archuleta County | 14,112 | 7 | 2 | 0 |
| Conejos County | 7,549 | 8 | 12 | 0 |
| Costilla County | 3,686 | 8 | 4 | 0 |
| Eagle County | 54,330 | 23 | 6 | 0 |
| Hinsdale County | 747 | 2 | 0 | 0 |
| Mineral County | 933 | 3 | 0 | 0 |
| Rio Grande County | 11,132 | 9 | 3 | 1 |
| Routt County | 25,243 | 25 | 31 | 0 |
| Saguache County | 6,670 | 5 | 3 | 0 |
| San Juan County | 821 | 1 | 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
- Florida
- Idaho
- 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.