Is King William County, VA a radon risk area?

EPA's own radon map rates King William County zone 3 - low potential, predicting a county-wide average indoor level below 2 pCi/L. That puts King William County in the 13th percentile nationally for radon potential — higher than 13% of the counties EPA has rated.

How King William County compares

About 19,232 people live in King William County, Virginia, spread over 273.91 square miles. That works out to roughly 70 people per square mile. Rank 636 by population within its EPA zone puts King William County at the 38th percentile among zone peers. King William County falls in EPA Radon Region 3, one of 245 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

A Zone 3 county like King William County is predicted closer to the 0.4 pCi/L typical outdoors than to EPA's 4 pCi/L action level. Low doesn't mean zero: EPA's own data shows homes in Zone 3 counties like King William County testing above the action level often enough that skipping a test isn't the safe assumption.

Next steps for a home in King William County

Nothing about King William 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 Virginia's state radon program

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

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