What EPA's radon map says about Petroleum County

Petroleum 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. Rank it against the rest of the country and Petroleum County lands in the 33rd percentile for radon potential.

Where Petroleum County sits nationally

About 525 people live in Petroleum County, Montana, spread over 1,655.625 square miles. That works out to roughly 0 people per square mile. Among counties sharing Petroleum County's EPA zone, it outranks 0% of them by population. EPA's geology-based Region 8 groups Petroleum County with 290 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Petroleum County's Zone 2 prediction clears the 1.3 pCi/L national indoor average without reaching EPA's own 4 pCi/L point for recommending a fix. A Zone 2 rating is a moderate county-wide average, not a guarantee about any one house in Petroleum County — testing is the only way to know an individual home's actual level.

Next steps for a home in Petroleum County

Mitigation cost doesn't depend on Petroleum 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

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

The methodology guide shows exactly which EPA and Census sources feed Petroleum County's numbers. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.