Boise County, ID: EPA's radon zone, explained

EPA's own radon map rates Boise County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. That puts Boise County in the 74th percentile nationally for radon potential — higher than 74% of the counties EPA has rated.

How Boise County compares

Boise County, Idaho is home to about 8,581 people across 1,899.368 square miles. Population density there runs about 5 people per square mile. By population, Boise County is the 807th largest of every county sharing its EPA zone — the 24th percentile by population within that zone. Geologically, Boise County is grouped into EPA Region 10 alongside 141 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

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

Next steps for a home in Boise County

For a Boise County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find Idaho's state radon program

For Boise County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Boise County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Use code RADONZONE-10OFF at checkout for 10% off.

Where Boise County's figures come from

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.