What EPA's radon map says about Marion County

EPA's own radon map rates Marion County zone 3 - low potential, predicting a county-wide average indoor level below 2 pCi/L. That puts Marion County in the 18th percentile nationally for radon potential — higher than 18% of the counties EPA has rated.

Where Marion County sits nationally

About 29,826 people live in Marion County, Tennessee, spread over 498.254 square miles. Averaged across its land area, Marion County runs about 60 people per square mile. Among counties sharing Marion County's EPA zone, it outranks 53% of them by population. Marion County falls in EPA Radon Region 4, one of 736 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Marion County's predicted average sits below the national indoor average of about 1.3 pCi/L, well under EPA's 4 pCi/L action level. Don't read Zone 3 as a pass for Marion County — EPA's guidance to test every home makes no exception for counties predicted low.

Testing and mitigation in Marion County

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 Tennessee'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. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.