What EPA's radon map says about Warren County

EPA's own radon map rates Warren County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. That puts Warren County in the 97th percentile nationally for radon potential — higher than 97% of the counties EPA has rated.

Warren County by the numbers

About 256,059 people live in Warren County, Ohio, spread over 401.415 square miles. Population density there runs about 638 people per square mile. Among counties sharing Warren County's EPA zone, it outranks 92% of them by population. EPA's geology-based Region 5 groups Warren County with 523 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Warren County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. Some Warren County homes will test comfortably under the action level despite the county's Zone 1 rating — the only way to know which kind of home you have is an actual test.

Next steps for a home in Warren County

Mitigation cost doesn't depend on Warren 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 Ohio'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

Warren County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.