Is Roosevelt County, MT a radon risk area?

EPA places Roosevelt 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. Nationally, Roosevelt County ranks higher in radon potential than 76% of rated counties (the 76th percentile).

Where Roosevelt County sits nationally

About 10,197 people live in Roosevelt County, Montana, spread over 2,354.602 square miles. Averaged across its land area, Roosevelt County runs about 4 people per square mile. Rank 757 by population within its EPA zone puts Roosevelt County at the 29th percentile among zone peers. Roosevelt 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

Roosevelt 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 Roosevelt County will test well under the action level, and EPA's guidance is to test regardless of zone.

Testing and mitigation in Roosevelt County

Nothing about Roosevelt 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

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

The methodology guide shows exactly which EPA and Census sources feed Roosevelt County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.