Is Kendall County, IL a radon risk area?

Kendall County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Kendall County sits at the 96th percentile nationally for radon potential — above 96 of every 100 rated counties.

Kendall County by the numbers

About 143,171 people live in Kendall County, Illinois, spread over 320.243 square miles. That works out to roughly 447 people per square mile. Rank 140 by population within its EPA zone puts Kendall County at the 87th percentile among zone peers. EPA's geology-based Region 5 groups Kendall County with 523 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Kendall County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. Being in Zone 1 raises the odds Kendall County homes test above the action level, but it does not mean any specific house does — EPA recommends every home be tested, in every zone, because the only way to know is to test.

If Kendall County tests above the action level

Nothing about Kendall 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

Kendall County's test kit answers today; a Airthings radon monitor keeps answering for Kendall County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.

More on how this number was built

Kendall County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Kendall County carries, the zone explainer covers what it does and doesn't tell you about any one house.