What EPA's radon map says about Plymouth County

Plymouth County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Nationally that's the 84th percentile for radon potential — Plymouth County outranks 84% of every county EPA has rated.

Where Plymouth County sits nationally

About 25,825 people live in Plymouth County, Iowa, spread over 862.828 square miles. That works out to roughly 30 people per square mile. Among counties sharing Plymouth County's EPA zone, it outranks 52% of them by population. Geologically, Plymouth County is grouped into EPA Region 7 alongside 411 other counties that share its rock and soil setting.

Zone vs. an actual test

Fixing a home becomes an EPA recommendation past 4 pCi/L, and that is precisely the side of the line Plymouth County's Zone 1 prediction lands on, well above the roughly 1.3 pCi/L most US homes average. Some Plymouth County homes will test comfortably under the action level despite the county's Zone 1 rating — the only way to know which kind of home you have is an actual test.

Next steps for a home in Plymouth County

Mitigation cost doesn't depend on Plymouth 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 Iowa's state radon program

Plymouth County's test kit answers today; a Airthings radon monitor keeps answering for Plymouth County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.

More on how this number was built

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.