Is Missoula County, MT a radon risk area?
EPA places Missoula County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Rank it against the rest of the country and Missoula County lands in the 95th percentile for radon potential.
Missoula County by the numbers
About 122,546 people live in Missoula County, Montana, spread over 2,593.01 square miles. Averaged across its land area, Missoula County runs about 47 people per square mile. Rank 161 by population within its EPA zone puts Missoula County at the 85th percentile among zone peers. EPA's geology-based Region 8 groups Missoula County with 290 other counties nationally sharing its underlying rock and soil profile.
What this actually means for a house in Missoula County
Missoula County carries a Zone 1 label because its predicted average clears 4 pCi/L outright — three-plus times the 0.4 pCi/L typical outdoors and above the 1.3 pCi/L most homes see. Some Missoula County homes will test comfortably under the action level despite the county's Zone 1 rating — the only way to know which kind of home you have is an actual test.
Next steps for a home in Missoula County
Nothing about Missoula County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.
Find Montana's state radon program
Missoula County's test kit answers today; a Airthings radon monitor keeps answering for Missoula County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.
More on how this number was built
Missoula County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.