What EPA's radon map says about Montgomery County

Montgomery County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Montgomery County sits at the 100th percentile nationally for radon potential — above 100 of every 100 rated counties.

Where Montgomery County sits nationally

About 879,190 people live in Montgomery County, Pennsylvania, spread over 482.937 square miles. That works out to roughly 1,821 people per square mile. Among counties sharing Montgomery County's EPA zone, it outranks 99% of them by population. Geologically, Montgomery County is grouped into EPA Region 3 alongside 244 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

Where the national indoor average runs about 1.3 pCi/L, Montgomery County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. 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 Montgomery County specifically.

Testing and mitigation in Montgomery County

Mitigation cost doesn't depend on Montgomery 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 Pennsylvania's state radon program

Montgomery County's test kit answers today; a Airthings radon monitor keeps answering for Montgomery 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 Montgomery County's numbers. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.