Lee County, IL: EPA's radon zone, explained

EPA's own radon map rates Lee County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Rank it against the rest of the country and Lee County lands in the 86th percentile for radon potential.

Lee County by the numbers

Lee County, Illinois is home to about 33,544 people across 724.769 square miles. Population density there runs about 46 people per square mile. By population, Lee County is the 439th largest of every county sharing its EPA zone — the 59th percentile by population within that zone. Lee County falls in EPA Radon Region 5, one of 524 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

Lee County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. Being in Zone 1 raises the odds Lee 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.

Next steps for a home in Lee County

For a Lee 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 Illinois's state radon program

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

Where Lee County's figures come from

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