What EPA's radon map says about Flathead County

Flathead County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Nationally, Flathead County ranks higher in radon potential than 95% of rated counties (the 95th percentile).

Flathead County by the numbers

About 114,527 people live in Flathead County, Montana, spread over 5,087.304 square miles. That works out to roughly 23 people per square mile. Among counties sharing Flathead County's EPA zone, it outranks 84% of them by population. Geologically, Flathead County is grouped into EPA Region 8 alongside 290 other counties that share its rock and soil setting.

Zone vs. an actual test

Fixing a home becomes an EPA recommendation past 4 pCi/L, and that is precisely the side of the line Flathead County's Zone 1 prediction lands on, well above the roughly 1.3 pCi/L most US homes average. EPA's guidance doesn't change because of a Zone 1 label: test the house. What changes is the reason to not put it off in Flathead County specifically.

Next steps for a home in Flathead County

Mitigation cost doesn't depend on Flathead County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find Montana's state radon program

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

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. Whatever zone Flathead County carries, the zone explainer covers what it does and doesn't tell you about any one house.