Is Lewis County, MO a radon risk area?

EPA's own radon map rates Lewis County zone 2 - moderate potential, predicting a county-wide average indoor level between 2 and 4 pCi/L. That puts Lewis County in the 40th percentile nationally for radon potential — higher than 40% of the counties EPA has rated.

How Lewis County compares

About 9,852 people live in Lewis County, Missouri, spread over 505.018 square miles. That works out to roughly 20 people per square mile. Rank 819 by population within its EPA zone puts Lewis County at the 21st percentile among zone peers. Lewis County falls in EPA Radon Region 7, one of 412 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Lewis County

EPA's Zone 2 rating for Lewis County sits below its own 4 pCi/L action level but above the national indoor average of about 1.3 pCi/L. Nothing about a Zone 2 label lowers the case for testing in Lewis County — EPA recommends it in every zone, moderate included.

Next steps for a home in Lewis County

Nothing about Lewis County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.

Find Missouri's state radon program

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

Lewis County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Lewis County carries, the zone explainer covers what it does and doesn't tell you about any one house.