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

LaSalle County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Rank it against the rest of the country and LaSalle County lands in the 94th percentile for radon potential.

LaSalle County by the numbers

LaSalle County, Illinois is home to about 108,390 people across 1,135.117 square miles. That works out to roughly 95 people per square mile. By population, LaSalle County is the 182nd largest of every county sharing its EPA zone — the 83rd percentile by population within that zone. Geologically, LaSalle County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

Zone vs. an actual test

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — LaSalle County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. 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 LaSalle County specifically.

Next steps for a home in LaSalle County

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

Where LaSalle County's figures come from

LaSalle County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.