Is Madison County, OH a radon risk area?

EPA's own radon map rates Madison County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Rank it against the rest of the country and Madison County lands in the 89th percentile for radon potential.

Where Madison County sits nationally

About 45,531 people live in Madison County, Ohio, spread over 466.688 square miles. Averaged across its land area, Madison County runs about 98 people per square mile. Rank 346 by population within its EPA zone puts Madison County at the 68th percentile among zone peers. Geologically, Madison County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

Madison County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. 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 Madison County specifically.

Next steps for a home in Madison County

Nothing about Madison 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

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

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