What EPA's radon map says about Marshall County

EPA places Marshall County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. That puts Marshall County in the 87th percentile nationally for radon potential — higher than 87% of the counties EPA has rated.

Where Marshall County sits nationally

About 37,847 people live in Marshall County, Tennessee, spread over 375.462 square miles. Averaged across its land area, Marshall County runs about 101 people per square mile. Among counties sharing Marshall County's EPA zone, it outranks 63% of them by population. Marshall County falls in EPA Radon Region 4, one of 736 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

Marshall County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. EPA's guidance doesn't change because of a Zone 1 label: test the house. What changes is the reason to not put it off in Marshall County specifically.

If Marshall County tests above the action level

Mitigation cost doesn't depend on Marshall 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

Marshall County's test kit answers today; a Airthings radon monitor keeps answering for Marshall 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

The methodology guide shows exactly which EPA and Census sources feed Marshall County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.