Madison County, MO: EPA's radon zone, explained

EPA places Madison County in Zone 2 - Moderate Potential — a predicted county-wide average indoor radon level between 2 and 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally, Madison County ranks higher in radon potential than 42% of rated counties (the 42nd percentile).

Madison County by the numbers

Madison County, Missouri is home to about 12,852 people across 494.386 square miles. Population density there runs about 26 people per square mile. By population, Madison County is the 763rd largest of every county sharing its EPA zone — the 26th percentile by population within that zone. Madison County falls in EPA Radon Region 7, one of 412 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

Madison County's Zone 2 prediction clears the 1.3 pCi/L national indoor average without reaching EPA's own 4 pCi/L point for recommending a fix. Nothing about a Zone 2 label lowers the case for testing in Madison County — EPA recommends it in every zone, moderate included.

Next steps for a home in Madison County

For a Madison 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 Missouri's state radon program

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

Where Madison County's figures come from

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