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Counties with the Highest Radon Potential in Colorado

The top 25 of 64 Colorado counties on GIS Map, ranked by EPA radon zone, where zone 1 carries the highest predicted indoor radon potential and zone 3 the lowest.

#CountyEPA radon zone
1Alamosa County
2
2Archuleta County
2
3Conejos County
2
4Costilla County
2
5Eagle County
2
6Hinsdale County
2
7Mineral County
2
8Rio Grande County
2
9Routt County
2
10Saguache County
2
11San Juan County
2
12Adams County
1
13Arapahoe County
1
14Baca County
1
15Bent County
1
16Boulder County
1
17Broomfield County
1
18Chaffee County
1
19Cheyenne County
1
20Clear Creek County
1
21Crowley County
1
22Custer County
1
23Delta County
1
24Denver County
1
25Dolores County
1

Source: EPA Map of Radon Zones (September 2025). All counties with data are ranked. Estimates carry margins of error.

Citing this page: GIS Map, “Counties with the Highest Radon Potential in Colorado”, https://gismap.land/rankings/colorado/highest-radon-counties. Figures from EPA Map of Radon Zones (September 2025).

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