Warren County, IA: EPA's radon zone, explained

EPA places Warren 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 Warren County in the 91st percentile nationally for radon potential — higher than 91% of the counties EPA has rated.

Warren County by the numbers

Warren County, Iowa is home to about 56,343 people across 569.658 square miles. Averaged across its land area, Warren County runs about 99 people per square mile. By population, Warren County is the 290th largest of every county sharing its EPA zone — the 73rd percentile by population within that zone. EPA's geology-based Region 7 groups Warren County with 411 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

Warren 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 Warren County specifically.

Next steps for a home in Warren County

For a Warren County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find Iowa's state radon program

For Warren County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Warren County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.

Where Warren County's figures come from

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.