Is Washington County, WI a radon risk area?

EPA places Washington County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally, Washington County ranks higher in radon potential than 95% of rated counties (the 95th percentile).

How Washington County compares

About 138,727 people live in Washington County, Wisconsin, spread over 430.644 square miles. That works out to roughly 322 people per square mile. Rank 146 by population within its EPA zone puts Washington County at the 86th percentile among zone peers. EPA's geology-based Region 5 groups Washington County with 523 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

Where the national indoor average runs about 1.3 pCi/L, Washington County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. 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 Washington County specifically.

Next steps for a home in Washington County

Nothing about Washington 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 Wisconsin's state radon program

Washington County's test kit answers today; a Airthings radon monitor keeps answering for Washington County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Use code RADONZONE-10OFF at checkout for 10% off.

More on how this number was built

Washington County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.