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 that's the 56th percentile for radon potential — Madison County outranks 56% of every county EPA has rated.

Madison County by the numbers

About 55,549 people live in Madison County, Idaho, spread over 469.267 square miles. Averaged across its land area, Madison County runs about 118 people per square mile. Among counties sharing Madison County's EPA zone, it outranks 68% of them by population. Madison County falls in EPA Radon Region 10, one of 142 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Madison County

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. Madison County's Zone 2 rating sits in the middle nationally; EPA's guidance is unchanged by that — test every home regardless of its zone.

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 Idaho'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. Code RADONZONE-10OFF takes 10% off at checkout.

More on how this number was built

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. Whatever zone Madison County carries, the zone explainer covers what it does and doesn't tell you about any one house.