What EPA's radon map says about Suffolk County

EPA places Suffolk County in Zone 3 - Low Potential — a predicted county-wide average indoor radon level below 2 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Suffolk County sits at the 32nd percentile nationally for radon potential — above 32 of every 100 rated counties.

How Suffolk County compares

About 793,144 people live in Suffolk County, Massachusetts, spread over 58.257 square miles. Averaged across its land area, Suffolk County runs about 13,615 people per square mile. Among counties sharing Suffolk County's EPA zone, it outranks 96% of them by population. Geologically, Suffolk County is grouped into EPA Region 1 alongside 58 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

At Zone 3, Suffolk County's predicted county average is under the national indoor average (~1.3 pCi/L) and well below EPA's 4 pCi/L action level — outdoor air nationally runs about 0.4 pCi/L for comparison. A Zone 3 label describes Suffolk County's average, not any one basement or slab in it — testing is still the only way an individual homeowner actually finds out.

Next steps for a home in Suffolk County

Mitigation cost doesn't depend on Suffolk 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

Suffolk County's test kit answers today; a Airthings radon monitor keeps answering for Suffolk 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 Suffolk County's numbers. Whatever zone Suffolk County carries, the zone explainer covers what it does and doesn't tell you about any one house.