What EPA's radon map says about Nez Perce County

Nez Perce County is mapped as Zone 3 - Low Potential by EPA — meaning the county-wide average indoor level is predicted below 2 pCi/L. Nationally that's the 21st percentile for radon potential — Nez Perce County outranks 21% of every county EPA has rated.

How Nez Perce County compares

About 42,847 people live in Nez Perce County, Idaho, spread over 848.32 square miles. Population density there runs about 51 people per square mile. Among counties sharing Nez Perce County's EPA zone, it outranks 63% of them by population. EPA's geology-based Region 10 groups Nez Perce County with 141 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

At Zone 3, Nez Perce County's predicted county average is under the national indoor average (~1.3 pCi/L) and well below EPA's 4 pCi/L action level — outdoor air nationally runs about 0.4 pCi/L for comparison. A Zone 3 rating means Nez Perce County's county-wide average is predicted low, but EPA is explicit that a meaningful share of homes in low-potential zones still test above the action level — a low zone is not a reason to skip testing.

Next steps for a home in Nez Perce County

Mitigation cost doesn't depend on Nez Perce 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 Idaho's state radon program

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

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