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Radon zones in Colorado

The EPA assigns every county in Colorado to one of three radon potential zones. 53 are in Zone 1, the highest category, home to about 98% of the state's residents.

64
Counties
53
Zone 1 counties
Predicted average above 4 pCi/L
11
Zone 2 counties
Predicted average 2-4 pCi/L
0
Zone 3 counties
Predicted average below 2 pCi/L

The map

Radon potential across Colorado

Every county in Colorado, filled by the zone the EPA assigns it. Zones follow geology rather than county lines, so the colour usually changes where the bedrock does, not where the border is.

Zone 1 · 53Zone 2 · 11Zone 3 · 0

Hover a county · click to open it

County by county

All 64 Colorado counties

Zone 1 · > 4 pCi/LZone 2 · 2 - 4 pCi/LZone 3 · < 2 pCi/L
CountyZonePopulationCOPDSmokingLung ca. deaths
Adams County1533k5.1%13.4%25.6
Arapahoe County1656k4.9%10.5%21.1
Baca County13,34410.7%16.9% -
Bent County15,68110.1%20.0% -
Boulder County1327k4.7%8.8%16.5
Broomfield County177k4.2%8.7%21.7
Chaffee County121k7.1%12.1%23.9
Cheyenne County11,7278.0%13.9% -
Clear Creek County19,1475.7%10.1% -
Crowley County15,6367.1%18.0% -
Custer County15,5348.6%12.2% -
Delta County132k9.2%14.5%24.8
Denver County1717k4.2%10.3%22.2
Dolores County12,5138.3%14.9% -
Douglas County1384k4.0%7.8%15.6
El Paso County1744k5.2%10.7%24.4
Elbert County129k5.9%11.2%23.1
Fremont County150k8.2%15.5%31.4
Garfield County163k5.8%12.2%17.3
Gilpin County15,9266.1%11.4% -
Grand County116k6.2%11.8% -
Gunnison County117k4.6%9.6% -
Huerfano County17,0558.6%12.9% -
Jackson County11,30910.6%16.9% -
Jefferson County1576k5.0%9.9%20.4
Kiowa County11,3848.9%13.8% -
Kit Carson County16,9948.3%14.5%30.7
La Plata County156k6.2%11.7%14.9
Lake County17,3654.7%10.2% -
Larimer County1371k5.2%9.6%18.6
Las Animas County114k8.2%13.7%29.0
Lincoln County15,4807.9%15.5% -
Logan County121k8.4%16.0%28.8
Mesa County1160k7.0%12.7%26.4
Moffat County113k7.9%15.6%29.1
Montezuma County127k8.3%14.7%25.1
Montrose County144k8.0%13.4%27.4
Morgan County130k6.9%13.8%26.8
Otero County118k9.0%15.3%29.9
Ouray County15,1766.2%9.1% -
Park County118k6.5%11.3%13.8
Phillips County14,4768.3%14.3% -
Pitkin County117k4.9%8.3% -
Prowers County112k8.1%15.0%44.9
Pueblo County1169k7.2%13.9%31.4
Rio Blanco County16,5696.8%13.1% -
San Miguel County17,8685.3%9.8% -
Sedgwick County12,2999.1%13.6% -
Summit County130k5.0%10.5% -
Teller County125k6.8%11.3%24.2
Washington County14,8557.6%13.4%42.6
Weld County1359k5.5%12.7%22.6
Yuma County19,8627.8%13.9% -
Alamosa County217k6.4%12.7%24.5
Archuleta County214k7.7%12.0%22.8
Conejos County27,5216.9%13.0% -
Costilla County23,6288.4%13.5% -
Eagle County254k5.0%10.3%10.8
Hinsdale County27656.0%8.4% -
Mineral County29446.9%10.5% -
Rio Grande County211k7.1%12.5% -
Routt County225k5.4%10.2%11.5
Saguache County26,6889.3%14.6% -
San Juan County28026.2%11.2% -

Zones from the EPA Map of Radon Zones. COPD and smoking are CDC PLACES model-based estimates of adult prevalence. Lung cancer death rates are age-adjusted deaths per 100,000 per year, 2019-2023, from NCI State Cancer Profiles. A dash means the source does not report a value for that county.

Highest potential

Zone 1 counties in Colorado

These 53 counties have a predicted average indoor radon screening level above the EPA action level. The EPA recommends every home in them be tested.

Other states

Radon zones elsewhere