What EPA's radon map says about Plymouth County

EPA's own radon map rates Plymouth County zone 2 - moderate potential, predicting a county-wide average indoor level between 2 and 4 pCi/L. Nationally, Plymouth County ranks higher in radon potential than 65% of rated counties (the 65th percentile).

Plymouth County by the numbers

About 542,090 people live in Plymouth County, Massachusetts, spread over 658.521 square miles. That works out to roughly 823 people per square mile. Among counties sharing Plymouth County's EPA zone, it outranks 96% of them by population. EPA's geology-based Region 1 groups Plymouth County with 58 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

EPA's Zone 2 rating for Plymouth County sits below its own 4 pCi/L action level but above the national indoor average of about 1.3 pCi/L. A county-wide moderate average, like Plymouth County's, can still hide a specific house well above or below it — testing is what actually answers the question.

Next steps for a home in Plymouth County

Mitigation cost doesn't depend on Plymouth 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 Massachusetts's state radon program

Plymouth County's test kit answers today; a Airthings radon monitor keeps answering for Plymouth County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.

More on how this number was built

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