Is Seneca County, OH a radon risk area?

EPA's own radon map rates Seneca County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally that's the 91st percentile for radon potential — Seneca County outranks 91% of every county EPA has rated.

How Seneca County compares

About 54,730 people live in Seneca County, Ohio, spread over 551.026 square miles. Averaged across its land area, Seneca County runs about 99 people per square mile. Rank 293 by population within its EPA zone puts Seneca County at the 73rd percentile among zone peers. EPA's geology-based Region 5 groups Seneca County with 523 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Seneca County

Seneca 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. Some Seneca 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.

If Seneca County tests above the action level

Nothing about Seneca 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 Ohio's state radon program

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

Seneca 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.