What EPA's radon map says about Madera County

EPA places Madera 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 that's the 61st percentile for radon potential — Madera County outranks 61% of every county EPA has rated.

Madera County by the numbers

About 165,432 people live in Madera County, California, spread over 2,136.709 square miles. That works out to roughly 77 people per square mile. Among counties sharing Madera County's EPA zone, it outranks 86% of them by population. Geologically, Madera County is grouped into EPA Region 9 alongside 94 other counties that share its rock and soil setting.

What this actually means for a house in Madera County

Madera 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). Middle-of-the-pack doesn't mean risk-free for any one Madera County address — a moderate county average still leaves individual homes to test either side of it.

If Madera County tests above the action level

Mitigation cost doesn't depend on Madera 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 California's state radon program

Madera County's test kit answers today; a Airthings radon monitor keeps answering for Madera 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

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