Washington County, OR radon potential

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. That puts Washington County in the 65th percentile nationally for radon potential — higher than 65% of the counties EPA has rated.

Washington County by the numbers

Washington County, Oregon is home to about 611,272 people across 724.272 square miles. Averaged across its land area, Washington County runs about 844 people per square mile. Within its own EPA zone, Washington County is bigger by population than 96% of the counties that share it. Washington County falls in EPA Radon Region 10, one of 142 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Washington County

Washington 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). 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.

Next steps for a home in Washington County

A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.

Find Oregon'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

Washington County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Washington County carries, the zone explainer covers what it does and doesn't tell you about any one house.