Is Union County, OH a radon risk area?

EPA's own radon map rates Union County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Union County sits at the 92nd percentile nationally for radon potential — above 92 of every 100 rated counties.

Union County by the numbers

About 71,721 people live in Union County, Ohio, spread over 431.713 square miles. Averaged across its land area, Union County runs about 166 people per square mile. Rank 244 by population within its EPA zone puts Union County at the 77th percentile among zone peers. EPA's geology-based Region 5 groups Union County with 523 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Union County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. That doesn't mean every Union County house tests high — a zone is a county-wide prediction, never a single-home reading — but it's a reason to test sooner rather than let it wait.

Testing and mitigation in Union County

Nothing about Union 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

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

Union County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Union County carries, the zone explainer covers what it does and doesn't tell you about any one house.