Short-term kit
RA100 short-term liquid scintillation radon test kit
- Lab fee extra
Method: Liquid scintillation
In home: 48 to 96 hours
Locations and reports
Radon Levels in Plymouth County, Massachusetts
EPA puts Plymouth County in Zone 2, its middle radon zone, and 17.0% of its 16,320 reported radon tests (2008 to 2017, laboratory totals) were at or above 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Share at 4+ pCi/L
17.0%
6.8 pts below MA
- Plymouth
- 17.0%
- MA
- 23.8%
16,320 tests, 2008 to 2017
Median result
1.7pCi/L
Below action level
- Plymouth
- 1.7 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
16,320
5th of 14 by tests
- Plymouth
- 16,320
- Middlesex
- 75,220
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
EPA predicts 2 to 4 pCi/L indoors
Rank in MA
11 of 14
Middle half
- Plymouth
- 17.0%
- Worcester
- 33.5%
By share, of 14 with 30+ tests
Read a result for Plymouth County
Starts at Plymouth County's median, 1.7 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 1.7 pCi/L
Below 2 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is below 2 pCi/L, the level at which EPA says a fix should be considered. Plymouth County's median reported result, 2008 to 2017.
The data
Plymouth County, At a glance
Plymouth County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Plymouth County is a
USGS geologic potential: Moderate across 98% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Plymouth County, 2008 to 2017, laboratory
Under 2 pCi/L: 56%2 to 4 pCi/L: 27%4 pCi/L and above: 17%
Of 16,320 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 9,184 | 56.3% |
| 2 to 4 pCi/L | 4,365 | 26.7% |
| 4 pCi/L and above | 2,771 | 17.0% |
What these figures count
These are the 16,320 tests reported to CDC for Plymouth County over 2008 to 2017 (laboratory totals), many from homes being sold or already suspected of a problem: they describe the county's reported tests, not this house.
Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).
Plymouth County, Compared
Plymouth County radon figures, compared
Calculated by Radon411Plymouth County's 16,320 reported tests over the 2008 to 2017 laboratory totals had a middle value of 1.7 pCi/L and a maximum of 182.9 pCi/L, and 17.0% reached 4 pCi/L. Massachusetts as a whole (14 Massachusetts counties, pooled) comes to 23.8%: 6.8 points higher than here.
Among its state's counties it ranks 11th of 14 Massachusetts counties with 30 or more tests for the same period. Statewide for the same period, Worcester County reported the highest share (33.5%) and Nantucket County the lowest (5.0%).
Below the action level, 9,184 tests (56.3%) came in under 2 pCi/L, against 49.6% statewide, and 4,365 tests (26.7%) fell between 2 and 4, against 26.6% statewide. CDC's ten-year totals for Plymouth County went from 14,428 tests (2005 to 2014) to 16,320 (2008 to 2017), the share going from 16.4% to 17.0%.
EPA's 1993 zone map puts Plymouth County in Zone 2, a predicted county average between 2 and 4 pCi/L. USGS geology rates 98% of the county's land moderate radon potential.
Next door, the shares run from 20.6% in Barnstable County to 23.2% in Bristol County.
CDC also counts 75 tests taken after mitigation in Plymouth County for the same period: tests in homes where a fix was already in.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Plymouth County, Geology
The ground under Plymouth County
PredictedMost of the ground under Plymouth County is one class on USGS's geologic map: 97.8% of its land is moderate radon potential, with 0.7% low. The map puts 66.2% of Plymouth County in the area it calls Esmond-Dedham terrane and 31.6% in Narrangansett Basin, with one smaller area beside them. USGS gives the first a radon index of 11 and the second 9, both in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Esmond-Dedham terrane | Granite plutons, mafic metasedimentary and metavolcanic rocks. | Moderate | 11 | 66.2% |
| Narrangansett Basin | Pennsylvanian sedimentary rocks. | Moderate | 9 | 31.6% |
| Boston Basin | Proterozoic to Pennsylvanian sedimentary rocks. | Low | 8 | 0.7% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Plymouth County beside the ground around it
Across Massachusetts 31.9% of the land is rated high; none of Plymouth County's is. Of the 3 counties that border it, 1 has more high-potential ground, Norfolk County the most at 7.0%.
The map rates the ground, not the air in any home.
Local help
Plymouth County, Local resources
Radon testing and mitigation in Plymouth County
- Radon UnitRadon Unit, run by Department of Public Health, answers questions about testing, mitigation and the rules in Massachusetts.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsAsk the program whether it has free or discounted kits, or compare kits you can buy.
- Compare kits
- Professionals in Massachusetts5 professionals are listed in Massachusetts.
What Massachusetts's program says
- Phone
- (800) 723-6695
- DPHIAQ.radon@mass.gov
What it means
Plymouth County, Questions
Questions about radon in Plymouth County
Are radon levels high in Plymouth County?
Over the 2008 to 2017 laboratory totals, 17.0% of the radon tests reported to CDC for Plymouth County, Massachusetts were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.7 pCi/L. Of 14 Massachusetts counties with 30 or more tests for the same period, 10 reported a higher share; pooled, the state comes to 23.8%.
Which counties border Plymouth County?
Plymouth County borders 3 counties: Bristol County, Norfolk County and Barnstable County.
Products
Plymouth County, Products
Testing a home in Plymouth County
In Plymouth County, 17.0% of 16,320 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 23.8% pooled across Massachusetts. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Plymouth County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Monitor
Wave Plus battery radon and air quality monitor
- C-NRPP 2024/25: Not included
- Battery
- Bluetooth
- App only
Method: Alpha spectrometry
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Plymouth County, Bordering counties
Counties bordering Plymouth County
Calculated by Radon411- Radon levels in Bristol CountyEPA zone 2
23.2%at or above 4 pCi/L
Median 2.0 pCi/L · 13,358 tests · 6.2 points above Plymouth County
- Radon levels in Norfolk CountyEPA zone 2
21.2%at or above 4 pCi/L
Median 1.8 pCi/L · 39,205 tests · 4.2 points above Plymouth County
- Radon levels in Barnstable CountyEPA zone 2
20.6%at or above 4 pCi/L
Median 2.0 pCi/L · 6,521 tests · 3.6 points above Plymouth County
Plymouth County, Cities and towns
Cities and towns in Plymouth County
The Census Bureau estimates 546,829 residents in Plymouth County for July 1, 2025, 18,416 more than in 2020 (+3.5%). That works out to 830 people per square mile of land. No town dominates: Brockton, the largest, has 106,134 residents, 19.4% of the total. Together its 2 incorporated places hold 24.8% of those residents; the other 75.2% live outside any of them. CDC's 16,320 reported tests for 2008 to 2017 work out to 29.8 per 1,000 residents (2025 estimate), close to Massachusetts' 32.7.
From Brockton to Bridgewater Town, CDC publishes no figure by town: each reads Plymouth County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Brockton | 106,134 | +0.6% | 19.4% |
| Bridgewater Town | 29,309 | +9.5% | 5.4% |
2 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025).
Plymouth County, Homes
Homes in Plymouth County
Of Plymouth County's 216,654 homes, 70% are detached houses, against 51% across Massachusetts; 12% are in buildings of five or more homes. Much of Plymouth County is recent building: 17% of its homes have gone up since 2000 and the middle year built is 1971, against 1963 for Massachusetts. Owners live in 78% of the occupied homes (Massachusetts: 63%), so for most households a test and a fix are their own to order.
| Homes | Plymouth County | Massachusetts |
|---|---|---|
| Housing units | 216,654 | 3,014,657 |
| Detached houses | 70% | 51% |
| In buildings of 5 or more | 12% | 22% |
| Mobile homes | 2% | 1% |
| Built before 1960 | 38% | 47% |
| Built since 2000 | 17% | 14% |
| Middle year built | 1971 | 1963 |
| Owner-occupied | 78% | 63% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.