Is Hill County, MT a radon risk area?

Hill County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Nationally that's the 80th percentile for radon potential — Hill County outranks 80% of every county EPA has rated.

How Hill County compares

About 16,065 people live in Hill County, Montana, spread over 2,899.396 square miles. That works out to roughly 6 people per square mile. Rank 640 by population within its EPA zone puts Hill County at the 40th percentile among zone peers. EPA's geology-based Region 8 groups Hill County with 290 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

Hill 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 Hill 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.

Testing and mitigation in Hill County

Nothing about Hill 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

Hill County's test kit answers today; a Airthings radon monitor keeps answering for Hill County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Use code RADONZONE-10OFF at checkout for 10% off.

More on how this number was built

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.