Is Defiance County, OH a radon risk area?

Defiance County is mapped as Zone 2 - Moderate Potential by EPA — meaning the county-wide average indoor level is predicted between 2 and 4 pCi/L. Rank it against the rest of the country and Defiance County lands in the 53rd percentile for radon potential.

Defiance County by the numbers

About 38,644 people live in Defiance County, Ohio, spread over 411.439 square miles. Averaged across its land area, Defiance County runs about 94 people per square mile. Rank 407 by population within its EPA zone puts Defiance County at the 61st percentile among zone peers. Geologically, Defiance County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

Zone vs. an actual test

Defiance County's predicted average falls between EPA's 4 pCi/L action level and the national indoor average of about 1.3 pCi/L (outdoor air runs roughly 0.4 pCi/L). Defiance County's Zone 2 rating sits in the middle nationally; EPA's guidance is unchanged by that — test every home regardless of its zone.

Testing and mitigation in Defiance County

Nothing about Defiance 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

Defiance County's test kit answers today; a Airthings radon monitor keeps answering for Defiance County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

More on how this number was built

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.