Radon in Massachusetts
About 1 in 4 homes tested in Massachusetts were at or above the EPA action level of 4 pCi/L.
- Below 2 pCi/L: 50%
- 2 to 4 pCi/L: 26%
- 4 pCi/L or more: 24%
The EPA puts 3 of Massachusetts's 14 counties in Zone 1, its highest radon category, 10 in Zone 2 and 1 in Zone 3.
Every county in Massachusetts
Sorted by the share of homes tested at or above 4 pCi/L. Select a county for local details and costs.
| County | Homes tested | At or above 4 | Median | EPA zone |
|---|---|---|---|---|
| Worcester County | 34% | 2.6 pCi/L | 1 | |
| Essex County | 29% | 2.2 pCi/L | 1 | |
| Berkshire County | 27% | 1.7 pCi/L | 2 | |
| Bristol County | 23% | 2.0 pCi/L | 2 | |
| Franklin County | 22% | 1.6 pCi/L | 2 | |
| Middlesex County | 22% | 1.9 pCi/L | 1 | |
| Norfolk County | 21% | 1.8 pCi/L | 2 | |
| Barnstable County | 21% | 2.0 pCi/L | 2 | |
| Hampshire County | 19% | 1.5 pCi/L | 2 | |
| Dukes County | 17% | 1.7 pCi/L | 2 | |
| Plymouth County | 17% | 1.7 pCi/L | 2 | |
| Hampden County | 13% | 1.3 pCi/L | 2 | |
| Suffolk County | 10% | 1.3 pCi/L | 3 | |
| Nantucket County | 17 tests | – | – | 2 |
"–" means fewer than 20 tests or no lab data, too few for a reliable figure.
Sources
- EPA Map of Radon Zones (public domain).
- CDC Environmental Public Health Tracking Network, radon tests from labs, 2008–2017. Pre-mitigation tests only.
Last updated October 2026. How we calculate these numbers.