Knox County, IL radon potential

EPA's own radon map rates Knox County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally, Knox County ranks higher in radon potential than 90% of rated counties (the 90th percentile).

How Knox County compares

Knox County, Illinois is home to about 48,716 people across 716.355 square miles. That works out to roughly 68 people per square mile. Within its own EPA zone, Knox County is bigger by population than 70% of the counties that share it. EPA's geology-based Region 5 groups Knox County with 523 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Where the national indoor average runs about 1.3 pCi/L, Knox County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Knox County will test well under the action level, and EPA's guidance is to test regardless of zone.

Next steps for a home in Knox County

A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.

Find Illinois's state radon program

For Knox County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Knox 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 Knox County's figures come from

Knox County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.