What EPA's radon map says about Jefferson County

EPA's own radon map rates Jefferson County zone 2 - moderate potential, predicting a county-wide average indoor level between 2 and 4 pCi/L. That puts Jefferson County in the 63rd percentile nationally for radon potential — higher than 63% of the counties EPA has rated.

How Jefferson County compares

About 231,888 people live in Jefferson County, Missouri, spread over 656.042 square miles. That works out to roughly 353 people per square mile. Among counties sharing Jefferson County's EPA zone, it outranks 90% of them by population. Jefferson County falls in EPA Radon Region 7, one of 412 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Jefferson County

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

Next steps for a home in Jefferson County

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 Missouri'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. Use code RADONZONE-10OFF at checkout for 10% off.

More on how this number was built

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