What EPA's radon map says about Marion County

Marion 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. Nationally that's the 64th percentile for radon potential — Marion County outranks 64% of every county EPA has rated.

Marion County by the numbers

About 428,905 people live in Marion County, Florida, spread over 1,588.443 square miles. That works out to roughly 270 people per square mile. Among counties sharing Marion County's EPA zone, it outranks 94% of them by population. Geologically, Marion County is grouped into EPA Region 4 alongside 735 other counties that share its rock and soil setting.

What this actually means for a house in Marion County

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

If Marion County tests above the action level

Mitigation cost doesn't depend on Marion 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 Florida's state radon program

Marion County's test kit answers today; a Airthings radon monitor keeps answering for Marion 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 Marion County's numbers. Whatever zone Marion County carries, the zone explainer covers what it does and doesn't tell you about any one house.