Is Carroll County, IL a radon risk area?

Carroll County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. That puts Carroll County in the 79th percentile nationally for radon potential — higher than 79% of the counties EPA has rated.

Where Carroll County sits nationally

About 15,444 people live in Carroll County, Illinois, spread over 445.406 square miles. Averaged across its land area, Carroll County runs about 35 people per square mile. Rank 650 by population within its EPA zone puts Carroll County at the 39th percentile among zone peers. Carroll County falls in EPA Radon Region 5, one of 524 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Carroll County

Where the national indoor average runs about 1.3 pCi/L, Carroll County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. That doesn't mean every Carroll County house tests high — a zone is a county-wide prediction, never a single-home reading — but it's a reason to test sooner rather than let it wait.

Next steps for a home in Carroll County

Nothing about Carroll County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.

Find Illinois's state radon program

Carroll County's test kit answers today; a Airthings radon monitor keeps answering for Carroll 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

The methodology guide shows exactly which EPA and Census sources feed Carroll County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.