Is Warren County, IL a radon risk area?

EPA places Warren County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Rank it against the rest of the country and Warren County lands in the 80th percentile for radon potential.

Where Warren County sits nationally

About 16,217 people live in Warren County, Illinois, spread over 542.36 square miles. That works out to roughly 30 people per square mile. Rank 637 by population within its EPA zone puts Warren County at the 40th percentile among zone peers. Geologically, Warren County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

Fixing a home becomes an EPA recommendation past 4 pCi/L, and that is precisely the side of the line Warren County's Zone 1 prediction lands on, well above the roughly 1.3 pCi/L most US homes average. EPA's guidance doesn't change because of a Zone 1 label: test the house. What changes is the reason to not put it off in Warren County specifically.

If Warren County tests above the action level

Nothing about Warren 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 Illinois's state radon program

Warren County's test kit answers today; a Airthings radon monitor keeps answering for Warren 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 Warren County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.