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

Calhoun County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. That puts Calhoun County in the 70th percentile nationally for radon potential — higher than 70% of the counties EPA has rated.

Where Calhoun County sits nationally

Calhoun County, Illinois is home to about 4,224 people across 253.829 square miles. Averaged across its land area, Calhoun County runs about 17 people per square mile. By population, Calhoun County is the 945th largest of every county sharing its EPA zone — the 11th percentile by population within that zone. Geologically, Calhoun County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

Where the national indoor average runs about 1.3 pCi/L, Calhoun County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. 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 Calhoun County specifically.

Testing and mitigation in Calhoun County

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

Where Calhoun County's figures come from

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