What EPA's radon map says about Madison County

EPA's own radon map rates Madison County zone 2 - moderate potential, predicting a county-wide average indoor level between 2 and 4 pCi/L. Nationally, Madison County ranks higher in radon potential than 63% of rated counties (the 63rd percentile).

Madison County by the numbers

About 263,017 people live in Madison County, Illinois, spread over 715.522 square miles. Population density there runs about 368 people per square mile. Among counties sharing Madison County's EPA zone, it outranks 91% of them by population. Geologically, Madison 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 Madison County

Call it a middle case: above the 1.3 pCi/L most US homes average, below the 4 pCi/L line EPA uses to recommend mitigation — that's Madison County's Zone 2 prediction. A county-wide moderate average, like Madison County's, can still hide a specific house well above or below it — testing is what actually answers the question.

Next steps for a home in Madison County

Mitigation cost doesn't depend on Madison County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find Illinois's state radon program

Madison County's test kit answers today; a Airthings radon monitor keeps answering for Madison County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.

More on how this number was built

The methodology guide shows exactly which EPA and Census sources feed Madison County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.