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

Hamilton County is mapped as Zone 2 - Moderate Potential by EPA — meaning the county-wide average indoor level is predicted between 2 and 4 pCi/L. Rank it against the rest of the country and Hamilton County lands in the 38th percentile for radon potential.

Where Hamilton County sits nationally

Hamilton County, Illinois is home to about 7,818 people across 434.653 square miles. Averaged across its land area, Hamilton County runs about 18 people per square mile. By population, Hamilton County is the 876th largest of every county sharing its EPA zone — the 15th percentile by population within that zone. Geologically, Hamilton County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

What this actually means for a house in Hamilton County

Hamilton County's predicted average falls between EPA's 4 pCi/L action level and the national indoor average of about 1.3 pCi/L (outdoor air runs roughly 0.4 pCi/L). Nothing about a Zone 2 label lowers the case for testing in Hamilton County — EPA recommends it in every zone, moderate included.

If Hamilton County tests above the action level

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

The methodology guide shows exactly which EPA and Census sources feed Hamilton County's numbers. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.