Williams County, OH: EPA's radon zone, explained

EPA's own radon map rates Williams County zone 2 - moderate potential, predicting a county-wide average indoor level between 2 and 4 pCi/L. Nationally that's the 52nd percentile for radon potential — Williams County outranks 52% of every county EPA has rated.

How Williams County compares

Williams County, Ohio is home to about 36,554 people across 420.66 square miles. That works out to roughly 87 people per square mile. By population, Williams County is the 430th largest of every county sharing its EPA zone — the 58th percentile by population within that zone. Williams County falls in EPA Radon Region 5, one of 524 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

Williams 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). Nothing about a Zone 2 label lowers the case for testing in Williams County — EPA recommends it in every zone, moderate included.

If Williams County tests above the action level

For a Williams County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find Ohio's state radon program

For Williams County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Williams County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Use code RADONZONE-10OFF at checkout for 10% off.

Where Williams County's figures come from

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.