Is Delaware County, OH a radon risk area?

EPA's own radon map rates Delaware County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally that's the 97th percentile for radon potential — Delaware County outranks 97% of every county EPA has rated.

Delaware County by the numbers

About 237,966 people live in Delaware County, Ohio, spread over 443.149 square miles. Averaged across its land area, Delaware County runs about 537 people per square mile. Rank 89 by population within its EPA zone puts Delaware County at the 92nd percentile among zone peers. EPA's geology-based Region 5 groups Delaware County with 523 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Delaware 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. 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 Delaware County specifically.

If Delaware County tests above the action level

Nothing about Delaware 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

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

The methodology guide shows exactly which EPA and Census sources feed Delaware County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.