What EPA's radon map says about Marshall County

EPA's own radon map rates Marshall County zone 3 - low potential, predicting a county-wide average indoor level below 2 pCi/L. Rank it against the rest of the country and Marshall County lands in the 11th percentile for radon potential.

Marshall County by the numbers

About 16,147 people live in Marshall County, Oklahoma, spread over 371.49 square miles. That works out to roughly 43 people per square mile. Among counties sharing Marshall County's EPA zone, it outranks 33% of them by population. EPA's geology-based Region 6 groups Marshall County with 502 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

At Zone 3, Marshall County's predicted county average is under the national indoor average (~1.3 pCi/L) and well below EPA's 4 pCi/L action level — outdoor air nationally runs about 0.4 pCi/L for comparison. Don't read Zone 3 as a pass for Marshall County — EPA's guidance to test every home makes no exception for counties predicted low.

Testing and mitigation in Marshall County

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 Oklahoma'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

Marshall County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.