Is Richland County, MT a radon risk area?

Richland 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 76th percentile for radon potential — Richland County outranks 76% of every county EPA has rated.

Richland County by the numbers

About 11,028 people live in Richland County, Montana, spread over 2,084.556 square miles. Population density there runs about 5 people per square mile. Rank 741 by population within its EPA zone puts Richland County at the 30th percentile among zone peers. Richland County falls in EPA Radon Region 8, one of 291 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

Richland 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. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Richland County will test well under the action level, and EPA's guidance is to test regardless of zone.

Next steps for a home in Richland County

Nothing about Richland 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

Richland County's test kit answers today; a Airthings radon monitor keeps answering for Richland 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. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.