Lewis County, ID radon potential

Lewis County is mapped as Zone 3 - Low Potential by EPA — meaning the county-wide average indoor level is predicted below 2 pCi/L. Rank it against the rest of the country and Lewis County lands in the 2nd percentile for radon potential.

Where Lewis County sits nationally

Lewis County, Idaho is home to about 3,728 people across 478.822 square miles. Population density there runs about 8 people per square mile. Within its own EPA zone, Lewis County is bigger by population than 7% of the counties that share it. Geologically, Lewis County is grouped into EPA Region 10 alongside 141 other counties that share its rock and soil setting.

Zone vs. an actual test

Well clear of both the 1.3 pCi/L national indoor average and EPA's 4 pCi/L action level, Lewis County's Zone 3 prediction is the low end of the scale. Low doesn't mean zero: EPA's own data shows homes in Zone 3 counties like Lewis County testing above the action level often enough that skipping a test isn't the safe assumption.

Testing and mitigation in Lewis County

A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.

Find Idaho's state radon program

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

Where Lewis County's figures come from

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