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Radon zones in Montana

The EPA assigns every county in Montana to one of three radon potential zones. 49 are in Zone 1, the highest category, home to about 84% of the state's residents.

56
Counties
49
Zone 1 counties
Predicted average above 4 pCi/L
7
Zone 2 counties
Predicted average 2-4 pCi/L
0
Zone 3 counties
Predicted average below 2 pCi/L

The map

Radon potential across Montana

Every county in Montana, 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 · 49Zone 2 · 7Zone 3 · 0

Hover a county · click to open it

County by county

All 56 Montana counties

Zone 1 · > 4 pCi/LZone 2 · 2 - 4 pCi/LZone 3 · < 2 pCi/L
CountyZonePopulationCOPDSmokingLung ca. deaths
Beaverhead County19,8857.5%13.1%30.6
Big Horn County113k10.0%24.7%40.0
Blaine County16,8999.3%20.8% -
Broadwater County18,0327.5%13.9% -
Carbon County111k8.0%13.4%20.7
Carter County11,4189.5%15.0% -
Cascade County185k7.5%14.4%33.2
Chouteau County15,8478.5%16.6%34.0
Custer County112k7.4%14.5%21.4
Daniels County11,6337.9%13.3% -
Dawson County18,8107.0%13.5% -
Deer Lodge County19,6739.8%17.0%31.2
Fallon County12,9947.4%14.3% -
Fergus County112k8.5%14.6%29.7
Flathead County1114k7.0%12.8%24.1
Gallatin County1126k4.5%9.7%17.2
Garfield County11,2118.6%14.8% -
Glacier County114k10.8%26.5%28.1
Granite County13,5959.0%14.3% -
Hill County116k8.5%18.2%48.8
Jefferson County113k7.0%12.7%40.1
Judith Basin County12,0939.4%14.9% -
Lake County133k8.8%15.5%30.8
Lewis and Clark County175k6.3%12.0%29.1
Liberty County11,97410.9%17.7% -
Lincoln County122k10.7%16.7%32.4
Madison County19,5217.3%12.2% -
McCone County11,6767.8%12.7% -
Meagher County12,0718.9%13.3% -
Mineral County15,0909.3%15.0%47.8
Missoula County1122k5.4%11.5%24.2
Park County118k7.6%13.5%23.4
Phillips County14,2498.6%15.1% -
Pondera County16,12510.3%19.1% -
Powder River County11,7438.3%13.3% -
Powell County17,1338.1%16.9% -
Prairie County11,11212.8%17.5% -
Ravalli County148k7.6%12.7%23.5
Richland County111k6.4%13.8%32.1
Roosevelt County110k9.6%23.4%36.3
Rosebud County18,1609.5%20.2% -
Sanders County114k10.8%16.6%31.1
Sheridan County13,4988.3%14.7% -
Silver Bow County136k7.6%14.1%27.7
Stillwater County19,1737.5%12.9%31.0
Teton County16,4308.1%14.1% -
Toole County15,1338.8%19.3% -
Valley County17,4748.4%14.1%30.4
Wibaux County19108.4%14.4% -
Golden Valley County283511.1%16.1% -
Musselshell County25,3089.2%15.4% -
Petroleum County25548.6%13.9% -
Sweet Grass County23,7637.7%13.0% -
Treasure County27728.7%13.1% -
Wheatland County22,05710.0%17.0% -
Yellowstone County2171k6.4%13.9%28.9

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 Montana

These 49 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