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

Washington 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. Nationally that's the 56th percentile for radon potential — Washington County outranks 56% of every county EPA has rated.

Washington County by the numbers

Washington County, Ohio is home to about 58,332 people across 632.162 square miles. That works out to roughly 92 people per square mile. By population, Washington County is the 311th largest of every county sharing its EPA zone — the 70th percentile by population within that zone. Geologically, Washington County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

What this actually means for a house in Washington County

Neither at the 4 pCi/L action level nor down at the roughly 1.3 pCi/L national indoor norm, Washington County's Zone 2 prediction lands in the gap between the two. Middle-of-the-pack doesn't mean risk-free for any one Washington County address — a moderate county average still leaves individual homes to test either side of it.

Testing and mitigation in Washington County

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

Where Washington 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. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.