Radon in Massachusetts: radon map by county

EPA's Map of Radon Zones puts 3 of Massachusetts's 14 counties in Zone 1 (predicted average indoor radon above 4 pCi/L), 10 in Zone 2 and 1 in Zone 3. Of 95,409 building tests that radon laboratories reported for 2008 to 2017, 23.6% were at or above EPA's 4 pCi/L action level, against 36.5% nationally (number 31 of 42 states with 1,000+ tests). The highest county share is Worcester County (33.5% of 16,822 tests).

counties in Zone 1 (above 4 pCi/L predicted)

counties in Zone 2 (2 to 4)

counties in Zone 3 (below 2)

23.6%

of 95,409 lab tests at or above 4 pCi/L

Radon by county in Massachusetts

EPA radon zone and radon test results for each county in Massachusetts
County	EPA zone	Lab tests	Median	4+ pCi/L
Barnstable County	Zone 2	2,947	2.0	20.6%
Berkshire County	Zone 2	760	1.7	27.1%
Bristol County	Zone 2	6,113	2.0	23.2%
Dukes County	Zone 2	135	1.7	17.4%
Essex County	Zone 1	8,627	2.2	28.7%
Franklin County	Zone 2	460	1.6	22.3%
Hampden County	Zone 2	1,737	1.3	13.1%
Hampshire County	Zone 2	1,292	1.5	18.8%
Middlesex County	Zone 1	30,142	1.9	22%
Nantucket County	Zone 2	17	1.8	5%
Norfolk County	Zone 2	15,708	1.8	21.2%
Plymouth County	Zone 2	6,993	1.7	17%
Suffolk County	Zone 3	3,656	1.3	10.4%
Worcester County	Zone 1	16,822	2.6	33.5%

Lab tests: buildings tested by radon laboratories, 2008 to 2017; median in pCi/L; “4+ pCi/L” is the share of tests at or above EPA's action level. n/a: no value on file (no tests, or too few to report).

What the zones mean

Zone 1 counties have a predicted average indoor radon screening level above 4 pCi/L, Zone 2 from 2 to 4 pCi/L and Zone 3 below 2 pCi/L. The prediction is from 1993 indoor measurements, geology, aerial radioactivity, soils and foundation types. EPA: “This map should not be used to determine if individual homes need to be tested.” EPA recommends fixing a home at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of exposure.

Radon in Massachusetts: questions

What radon zone is Massachusetts?

EPA's 1993 map does not give states one zone; it zones each county. In Massachusetts, 3 counties are Zone 1, 10 Zone 2 and 1 Zone 3. EPA says the map "should not be used to determine if individual homes need to be tested".

Which Massachusetts counties have the highest radon levels?

By the share of laboratory tests at or above 4 pCi/L for 2008 to 2017 (counties with 20 or more tests): Worcester County 33.5% (median 2.6 pCi/L, 16,822 tests); Essex County 28.7% (median 2.2 pCi/L, 8,627 tests); Berkshire County 27.1% (median 1.7 pCi/L, 760 tests); Bristol County 23.2% (median 2.0 pCi/L, 6,113 tests); Franklin County 22.3% (median 1.6 pCi/L, 460 tests).

How common is high radon in Massachusetts?

23.6% of the 95,409 tests in the laboratory data for Massachusetts (2008 to 2017) were at or above 4 pCi/L; the national share was 36.5%. Buildings are tested by choice, often because of a sale or a concern, so the share describes the tests on file, not every home.

Should I test for radon in Massachusetts?

Yes. EPA recommends testing every home no matter where it is, fixing it at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of radon exposure.

States bordering Massachusetts

Radon in Connecticut (3 of 9 in Zone 1)Radon in New Hampshire (1 of 10 in Zone 1)Radon in New York (34 of 62 in Zone 1)Radon in Rhode Island (2 of 5 in Zone 1)Radon in Vermont (0 of 14 in Zone 1)

Other free hazard lookups

All of these, plus wetlands, FEMA hazard ratings and the federal contamination lists, are in the Environmental Records Report for any US address ($29).

Superfund sites in Massachusetts · Radon map of every state

Data compiled 2026-10-20. County-level screening information, not a radon measurement of any building.