Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Middlesex County, Massachusetts
EPA puts Middlesex County in Zone 1, its highest radon zone, and 22.0% of its 75,220 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
22.0%
1.8 pts below MA
- Middlesex
- 22.0%
- MA
- 23.8%
75,220 tests, 2008 to 2017
Median result
1.9pCi/L
Below action level
- Middlesex
- 1.9 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
75,220
Most tested in MA
- Middlesex
- 75,220
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in MA
6 of 14
Middle half
- Middlesex
- 22.0%
- Worcester
- 33.5%
By share, of 14 with 30+ tests
Read a result for Middlesex County
Starts at Middlesex County's median, 1.9 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 1.9 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. Middlesex County's median reported result, 2008 to 2017.
The data
Middlesex County, At a glance
Middlesex County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Middlesex County in
USGS geologic potential: High across 83% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Middlesex County, 2008 to 2017, laboratory
Under 2 pCi/L: 51%2 to 4 pCi/L: 27%4 pCi/L and above: 22%
Of 75,220 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 38,148 | 50.7% |
| 2 to 4 pCi/L | 20,556 | 27.3% |
| 4 pCi/L and above | 16,516 | 22.0% |
What these figures count
These are the 75,220 tests reported to CDC for Middlesex 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).
Middlesex County, Compared
Middlesex County radon figures, compared
Calculated by Radon411Middlesex County's 75,220 reported tests over the 2008 to 2017 laboratory totals had a middle value of 1.9 pCi/L and a maximum of 880.0 pCi/L, and 22.0% reached 4 pCi/L. Massachusetts as a whole (14 Massachusetts counties, pooled) comes to 23.8%: 1.8 points higher than here.
Among its state's counties it ranks 6th 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, 38,148 tests (50.7%) came in under 2 pCi/L, against 49.6% statewide, and 20,556 tests (27.3%) fell between 2 and 4, against 26.6% statewide. CDC's ten-year totals for Middlesex County went from 77,010 tests (2005 to 2014) to 75,220 (2008 to 2017), the share going from 21.2% to 22.0%.
EPA's 1993 zone map puts Middlesex County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 83% of the county's land high radon potential.
Next door, the shares run from 10.4% in Suffolk County to 34.4% in Hillsborough County, NH, with Norfolk County and Suffolk County below Middlesex County.
CDC also counts 506 tests taken after mitigation in Middlesex 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.
Middlesex County, Geology
The ground under Middlesex County
PredictedMost of the ground under Middlesex County is one class on USGS's geologic map: 82.6% of its land is high radon potential, with 10.4% moderate and 7.0% low. The map puts 52.9% of Middlesex County in the area it calls Nashoba and Rhode Island Terranes and 26.5% in Merrimack Belt, with 3 smaller areas beside them. USGS gives the first a radon index of 13 and the second 14, both in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Nashoba and Rhode Island Terranes | Granitic plutonic rocks and metamorphic rocks. | High | 13 | 52.9% |
| Merrimack Belt | Granitic plutons, metasedimentary rocks (phyllites, carbonaceous slates and schists). | High | 14 | 26.5% |
| Newbury Basin | Rhyolite, andesite, tuff, basalt, siltstone, mudstone. | Moderate | 10 | 10.4% |
| Boston Basin | Proterozoic to Pennsylvanian sedimentary rocks. | Low | 8 | 7.0% |
| Cape Ann and Peabody plutons | Felsic granitic rocks and lesser exposures of mafic plutonic rocks. | High | 13 | 3.2% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Middlesex County beside the ground around it
Middlesex County has more high-potential ground than Massachusetts as a whole: 82.6% of its land against 31.9%. Of the 5 counties that border it, 2 have more high-potential ground, Essex County the most at 86.7%.
The map rates the ground, not the air in any home.
Local help
Middlesex County, Local resources
Radon testing and mitigation in Middlesex 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
Middlesex County, Questions
Questions about radon in Middlesex County
Are radon levels high in Middlesex County?
Over the 2008 to 2017 laboratory totals, 22.0% of the radon tests reported to CDC for Middlesex County, Massachusetts were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.9 pCi/L. Of 14 Massachusetts counties with 30 or more tests for the same period, 5 reported a higher share; pooled, the state comes to 23.8%.
Which counties border Middlesex County?
Middlesex County borders 5 counties: Suffolk County, MA, Norfolk County, MA, Essex County, MA, Worcester County, MA and Hillsborough County, NH.
Products
Middlesex County, Products
Testing a home in Middlesex County
In Middlesex County, 22.0% of 75,220 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 23.8% pooled across Massachusetts. In Zone 1 the year-round level in Middlesex County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.
Test kits and monitors3
See every kit and monitor
MonitorAEGTEST
HOUND-1011S rechargeable radon detector with a screen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
First reading: Within 12 hours
Short-term kit
PicoCan short-term charcoal canister radon test
- Lab fee included
Method: Charcoal
In home: 48 to 96 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Middlesex County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Middlesex County
Explore
Middlesex County, Bordering counties
Counties bordering Middlesex County
Calculated by Radon411- Radon levels in Hillsborough County, NHEPA zone 2
34.4%at or above 4 pCi/L
Median 2.5 pCi/L · 5,528 tests · 12.4 points above Middlesex County
- Radon levels in Worcester County, MAEPA zone 1
33.5%at or above 4 pCi/L
Median 2.6 pCi/L · 46,440 tests · 11.5 points above Middlesex County
- Radon levels in Essex County, MAEPA zone 1
28.7%at or above 4 pCi/L
Median 2.2 pCi/L · 20,398 tests · 6.7 points above Middlesex County
- Radon levels in Norfolk County, MAEPA zone 2
21.2%at or above 4 pCi/L
Median 1.8 pCi/L · 39,205 tests · 0.8 points below Middlesex County
- Radon levels in Suffolk County, MAEPA zone 3
10.4%at or above 4 pCi/L
Median 1.3 pCi/L · 8,525 tests · 11.6 points below Middlesex County
Middlesex County, Cities and towns
Cities and towns in Middlesex County
The Census Bureau estimates 1,669,979 residents in Middlesex County for July 1, 2025, 45,518 more than in 2020 (+2.8%). Packed into its land, that is 2,042 people per square mile. No town dominates: Cambridge, the largest, has 122,588 residents, 7.3% of the total. CDC's 75,220 reported tests for 2008 to 2017 work out to 45.0 per 1,000 residents (2025 estimate), close to Massachusetts' 32.7.
From Cambridge to Watertown Town, CDC publishes no figure by town: each reads Middlesex County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Cambridge | 122,588 | +5.5% | 7.3% |
| Lowell | 119,971 | +3.6% | 7.2% |
| Newton | 90,741 | +2.2% | 5.4% |
| Somerville | 84,211 | +4.3% | 5.0% |
| Framingham | 73,021 | +1.3% | 4.4% |
| Malden | 66,370 | +0.5% | 4.0% |
| Waltham | 65,037 | +1.3% | 3.9% |
| Medford | 59,834 | +0.4% | 3.6% |
| Everett | 53,572 | +9.5% | 3.2% |
| Woburn | 43,962 | +7.8% | 2.6% |
| Marlborough | 42,772 | +2.7% | 2.6% |
| Melrose | 29,597 | −0.4% | 1.8% |
- Watertown Town
13 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).
Middlesex County, Homes
Homes in Middlesex County
Fewer than six in ten of Middlesex County's 660,814 homes are detached houses (47%, against 51% across Massachusetts); the rest are attached, in shared buildings or mobile. Half of its homes were built before 1961, close to Massachusetts' 1963: 48% date from before 1960 and 14% from 2000 or later. 62% of occupied homes are lived in by their owner (Massachusetts: 63%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Middlesex County | Massachusetts |
|---|---|---|
| Housing units | 660,814 | 3,014,657 |
| Detached houses | 47% | 51% |
| In buildings of 5 or more | 25% | 22% |
| Mobile homes | under 1% | 1% |
| Built before 1960 | 48% | 47% |
| Built since 2000 | 14% | 14% |
| Middle year built | 1961 | 1963 |
| Owner-occupied | 62% | 63% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.