Is Yellowstone County, MT a radon risk area?

Yellowstone County is mapped as Zone 2 - Moderate Potential by EPA — meaning the county-wide average indoor level is predicted between 2 and 4 pCi/L. Yellowstone County sits at the 62nd percentile nationally for radon potential — above 62 of every 100 rated counties.

Where Yellowstone County sits nationally

About 171,583 people live in Yellowstone County, Montana, spread over 2,633.402 square miles. Population density there runs about 65 people per square mile. Rank 137 by population within its EPA zone puts Yellowstone County at the 87th percentile among zone peers. Yellowstone County falls in EPA Radon Region 8, one of 291 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Yellowstone County

EPA's Zone 2 rating for Yellowstone County sits below its own 4 pCi/L action level but above the national indoor average of about 1.3 pCi/L. Nothing about a Zone 2 label lowers the case for testing in Yellowstone County — EPA recommends it in every zone, moderate included.

Next steps for a home in Yellowstone County

Nothing about Yellowstone 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

Yellowstone County's test kit answers today; a Airthings radon monitor keeps answering for Yellowstone 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

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.