Franklin County, MA: EPA's radon zone, explained

Franklin County is mapped as Zone 2 - Moderate Potential by EPA — meaning the county-wide average indoor level is predicted between 2 and 4 pCi/L. That puts Franklin County in the 58th percentile nationally for radon potential — higher than 58% of the counties EPA has rated.

How Franklin County compares

Franklin County, Massachusetts is home to about 70,871 people across 699.209 square miles. That works out to roughly 101 people per square mile. By population, Franklin County is the 259th largest of every county sharing its EPA zone — the 75th percentile by population within that zone. Franklin County falls in EPA Radon Region 1, one of 59 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Franklin County

Franklin 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. A county-wide moderate average, like Franklin County's, can still hide a specific house well above or below it — testing is what actually answers the question.

If Franklin County tests above the action level

For a Franklin County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find Massachusetts's state radon program

For Franklin County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Franklin County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

Where Franklin County's figures come from

Franklin County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.