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

EPA's own radon map rates Rock County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Rock County sits at the 96th percentile nationally for radon potential — above 96 of every 100 rated counties.

How Rock County compares

Rock County, Wisconsin is home to about 165,461 people across 718.168 square miles. Averaged across its land area, Rock County runs about 230 people per square mile. By population, Rock County is the 121st largest of every county sharing its EPA zone — the 89th percentile by population within that zone. EPA's geology-based Region 5 groups Rock County with 523 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Where the national indoor average runs about 1.3 pCi/L, Rock County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Rock County will test well under the action level, and EPA's guidance is to test regardless of zone.

Testing and mitigation in Rock County

For a Rock 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 Rock County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Rock 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 Rock 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. Whatever zone Rock County carries, the zone explainer covers what it does and doesn't tell you about any one house.