What EPA's radon map says about Jefferson County

Jefferson County is mapped as Zone 3 - Low Potential by EPA — meaning the county-wide average indoor level is predicted below 2 pCi/L. Jefferson County sits at the 4th percentile nationally for radon potential — above 4 of every 100 rated counties.

Jefferson County by the numbers

About 6,900 people live in Jefferson County, Mississippi, spread over 519.933 square miles. Averaged across its land area, Jefferson County runs about 13 people per square mile. Among counties sharing Jefferson County's EPA zone, it outranks 12% of them by population. EPA's geology-based Region 4 groups Jefferson County with 735 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Jefferson County

Jefferson County's Zone 3 prediction undercuts the roughly 1.3 pCi/L most US homes average, nowhere near EPA's 4 pCi/L threshold for recommending mitigation. Low doesn't mean zero: EPA's own data shows homes in Zone 3 counties like Jefferson County testing above the action level often enough that skipping a test isn't the safe assumption.

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 Mississippi'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.