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

EPA's own radon map rates Coles County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally, Coles County ranks higher in radon potential than 89% of rated counties (the 89th percentile).

Coles County by the numbers

Coles County, Illinois is home to about 46,423 people across 508.272 square miles. Averaged across its land area, Coles County runs about 91 people per square mile. By population, Coles County is the 335th largest of every county sharing its EPA zone — the 69th percentile by population within that zone. Geologically, Coles County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

Zone vs. an actual test

Coles County carries a Zone 1 label because its predicted average clears 4 pCi/L outright — three-plus times the 0.4 pCi/L typical outdoors and above the 1.3 pCi/L most homes see. 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 Coles County will test well under the action level, and EPA's guidance is to test regardless of zone.

If Coles County tests above the action level

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

Where Coles County's figures come from

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.