Green County, WI: EPA's radon zone, explained

EPA's own radon map rates Green County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Green County sits at the 87th percentile nationally for radon potential — above 87 of every 100 rated counties.

How Green County compares

Green County, Wisconsin is home to about 37,183 people across 584.044 square miles. That works out to roughly 64 people per square mile. By population, Green County is the 404th largest of every county sharing its EPA zone — the 62nd percentile by population within that zone. EPA's geology-based Region 5 groups Green County with 523 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Green County

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Green County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. Some Green 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.

Testing and mitigation in Green County

For a Green 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 Wisconsin's state radon program

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

Where Green 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.