What EPA's radon map says about Madison County

EPA's own radon map rates Madison County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally that's the 75th percentile for radon potential — Madison County outranks 75% of every county EPA has rated.

Madison County by the numbers

About 9,753 people live in Madison County, Montana, spread over 3,588.156 square miles. Averaged across its land area, Madison County runs about 3 people per square mile. Among counties sharing Madison County's EPA zone, it outranks 28% of them by population. Madison County falls in EPA Radon Region 8, one of 291 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Fixing a home becomes an EPA recommendation past 4 pCi/L, and that is precisely the side of the line Madison County's Zone 1 prediction lands on, well above the roughly 1.3 pCi/L most US homes average. 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 Madison County specifically.

Testing and mitigation 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 Montana'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. Use code RADONZONE-10OFF at checkout for 10% off.

More on how this number was built

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.