What EPA's radon map says about Jefferson County

EPA's own radon map rates Jefferson County zone 3 - low potential, predicting a county-wide average indoor level below 2 pCi/L. That puts Jefferson County in the 19th percentile nationally for radon potential — higher than 19% of the counties EPA has rated.

Jefferson County by the numbers

About 33,944 people live in Jefferson County, Washington, spread over 1,803.728 square miles. Averaged across its land area, Jefferson County runs about 19 people per square mile. Among counties sharing Jefferson County's EPA zone, it outranks 57% of them by population. EPA's geology-based Region 10 groups Jefferson County with 141 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

Well clear of both the 1.3 pCi/L national indoor average and EPA's 4 pCi/L action level, Jefferson County's Zone 3 prediction is the low end of the scale. Even at Zone 3, Jefferson County homes are not guaranteed a low reading — zone is a county-wide average, and EPA recommends testing every home regardless of zone.

If Jefferson County tests above the action level

Mitigation cost doesn't depend on Jefferson County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find Washington's state radon program

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

More on how this number was built

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.