Is Stephenson County, IL a radon risk area?

EPA's own radon map rates Stephenson County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally that's the 89th percentile for radon potential — Stephenson County outranks 89% of every county EPA has rated.

Where Stephenson County sits nationally

About 43,088 people live in Stephenson County, Illinois, spread over 564.247 square miles. Averaged across its land area, Stephenson County runs about 76 people per square mile. Rank 358 by population within its EPA zone puts Stephenson County at the 66th percentile among zone peers. Geologically, Stephenson County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

Where the national indoor average runs about 1.3 pCi/L, Stephenson County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. 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 Stephenson County specifically.

Testing and mitigation in Stephenson County

Nothing about Stephenson 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

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

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.