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 Montgomery County, Maryland
EPA puts Montgomery County in Zone 1, its highest radon zone, and 18.0% of its 10,969 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
18.0%
5.9 pts below MD
- Montgomery
- 18.0%
- Maryland
- 23.9%
10,969 tests, 2008 to 2017
Median result
1.3pCi/L
Below action level
- Montgomery
- 1.3 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
10,969
Most tested in Maryland
- Montgomery
- 10,969
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 Maryland
15 of 19
Lowest quarter
- Montgomery
- 18.0%
- Washington
- 56.0%
By share, of 19 with 30+ tests
Read a result for Montgomery County
Starts at Montgomery County's median, 1.3 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 1.3 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. Montgomery County's median reported result, 2008 to 2017.
The data
Montgomery County, At a glance
Montgomery County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Montgomery County in
USGS geologic potential: High across 80% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Montgomery County, 2008 to 2017, laboratory
Under 2 pCi/L: 62%2 to 4 pCi/L: 20%4 pCi/L and above: 18%
Of 10,969 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 6,810 | 62.1% |
| 2 to 4 pCi/L | 2,187 | 19.9% |
| 4 pCi/L and above | 1,972 | 18.0% |
What these figures count
These are the 10,969 tests reported to CDC for Montgomery 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).
Montgomery County, Compared
Montgomery County radon figures, compared
Calculated by Radon411Montgomery County's 10,969 reported tests over the 2008 to 2017 laboratory totals had a middle value of 1.3 pCi/L and a maximum of 1287.1 pCi/L, and 18.0% reached 4 pCi/L. Maryland as a whole (24 Maryland counties, pooled) comes to 23.9%: 5.9 points higher than here.
Among its state's counties it ranks 15th of 19 Maryland counties with 30 or more tests for the same period. Statewide for the same period, Washington County reported the highest share (56.0%) and Wicomico County the lowest (0.0%).
Below the action level, 6,810 tests (62.1%) came in under 2 pCi/L, against 56.6% statewide, and 2,187 tests (19.9%) fell between 2 and 4, against 19.5% statewide. CDC's ten-year totals for Montgomery County went from 7,943 tests (2005 to 2014) to 10,969 (2008 to 2017), the share going from 17.2% to 18.0%.
EPA's 1993 zone map puts Montgomery County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 80% of the county's land high radon potential.
Next door, the shares run from 8.7% in District of Columbia, DC to 30.8% in Howard County, with Arlington County, VA and District of Columbia, DC below Montgomery County.
CDC also counts 487 tests taken after mitigation in Montgomery 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.
Montgomery County, Geology
The ground under Montgomery County
PredictedMost of the ground under Montgomery County is one class on USGS's geologic map: 80.2% of its land is high radon potential, with 19.8% moderate. The map puts 64.0% of Montgomery County in the area it calls Eastern Piedmont and 15.8% in Western Piedmont, with 2 smaller areas beside them. USGS gives the first a radon index of 12 and the second 15, both in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Eastern Piedmont | Precambrian igneous and metamorphic rocks (schist and gneiss). | High | 12 | 64.0% |
| Western Piedmont | Precambrian phyllitic metamorphic rocks. | High | 15 | 15.8% |
| Mesozoic Basins | Triassic-Jurassic shale, sandstone, conglomerate, and intrusive igneous rocks. | Moderate | 11 | 14.8% |
| Western Shore | Cretaceous, Quaternary, minor Tertiary gravel, sand, silt, clay. | Moderate | 10 | 4.5% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Montgomery County beside the ground around it
Montgomery County has more high-potential ground than Maryland as a whole: 80.2% of its land against 36.7%. Of the 7 counties that border it, 1 has more high-potential ground, Howard County the most at 91.2%.
The map rates the ground, not the air in any home.
Local help
Montgomery County, Local resources
Radon testing and mitigation in Montgomery County
- Maryland's radon programMaryland Department of HealthMaryland's radon program offers free or discounted test kits, and answers questions about testing and mitigation in Maryland.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Maryland residents may be eligible for a free radon test kit.
- Compare kits
- Professionals in Maryland5 professionals are listed in Maryland.
What Maryland's program says
- Phone
- 1-866-703-3266
What it means
Montgomery County, Questions
Questions about radon in Montgomery County
Are radon levels high in Montgomery County?
Over the 2008 to 2017 laboratory totals, 18.0% of the radon tests reported to CDC for Montgomery County, Maryland were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.3 pCi/L. Of 19 Maryland counties with 30 or more tests for the same period, 14 reported a higher share; pooled, the state comes to 23.9%.
Which counties border Montgomery County?
Montgomery County borders 7 counties: Howard County, MD, Arlington County, VA, District of Columbia, DC, Loudoun County, VA, Fairfax County, VA, Frederick County, MD and Prince George's County, MD.
Products
Montgomery County, Products
Testing a home in Montgomery County
In Montgomery County, 18.0% of 10,969 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 23.9% pooled across Maryland. In Zone 1 the year-round level in Montgomery 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
Monitor
RM-63Pro rechargeable radon monitor with a touchscreen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
Short-term kitKidde
442020 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 3 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Montgomery County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Montgomery County
Explore
Montgomery County, Bordering counties
Counties bordering Montgomery County
Calculated by Radon411- Radon levels in Howard County, MDEPA zone 1
30.8%at or above 4 pCi/L
Median 2.0 pCi/L · 4,549 tests · 12.8 points above Montgomery County
- Radon levels in Frederick County, MDEPA zone 1
28.1%at or above 4 pCi/L
Median 1.5 pCi/L · 3,933 tests · 10.1 points above Montgomery County
- Radon levels in Loudoun County, VAEPA zone 2
27.4%at or above 4 pCi/L
Median 1.8 pCi/L · 4,457 tests · 9.4 points above Montgomery County
19.0%at or above 4 pCi/L
Median 1.4 pCi/L · 1,603 tests · 1.0 points above Montgomery County
- Radon levels in Fairfax County, VAEPA zone 1
18.7%at or above 4 pCi/L
Median 1.5 pCi/L · 8,657 tests · 0.7 points above Montgomery County
- Radon levels in Arlington County, VAEPA zone 2
13.7%at or above 4 pCi/L
Median 1.4 pCi/L · 1,101 tests · 4.3 points below Montgomery County
- Radon levels in District of Columbia, DCEPA zone 3
8.7%at or above 4 pCi/L
Median 1.2 pCi/L · 2,126 tests · 9.3 points below Montgomery County
Montgomery County, Cities and towns
Cities and towns in Montgomery County
The Census Bureau estimates 1,074,582 residents in Montgomery County for July 1, 2025, 13,656 more than in 2020 (+1.3%). Packed into its land, that is 2,179 people per square mile. No town dominates: Gaithersburg, the largest, has 71,113 residents, 6.6% of the total. Together its 19 incorporated places hold 16.5% of those residents; the other 83.5% live outside any of them. CDC's 10,969 reported tests for 2008 to 2017 work out to 10.2 per 1,000 residents (2025 estimate), close to Maryland's 7.7.
From Gaithersburg to Barnesville, CDC publishes no figure by town: each reads Montgomery County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Gaithersburg | 71,113 | +2.4% | 6.6% |
| Rockville | 67,563 | +0.4% | 6.3% |
| Takoma Park | 17,260 | −1.8% | 1.6% |
| Poolesville | 5,942 | +2.8% | 0.6% |
| Chevy Chase | 2,804 | −3.0% | 0.3% |
| Kensington | 2,652 | +25.7% | 0.2% |
| Chevy Chase Village | 1,978 | −2.9% | 0.2% |
| Somerset | 1,151 | −3.3% | 0.1% |
| Garrett Park | 959 | −2.6% | Under 0.1% |
| Chevy Chase View | 952 | −2.7% | Under 0.1% |
| Martin's Additions | 879 | −4.5% | Under 0.1% |
| Chevy Chase Section Three | 773 | −2.4% | Under 0.1% |
- North Chevy Chase
- Chevy Chase Section Five
- Laytonsville
- Washington Grove
- Glen Echo
- Brookeville
- Barnesville
19 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).
Montgomery County, Homes
Homes in Montgomery County
Montgomery County has 405,127 homes, and many share a building: 33% are in buildings of five or more, 47% are detached houses, against 51% across Maryland. Half of its homes were built before 1980, close to Maryland's 1979: 20% date from before 1960 and 20% from 2000 or later. 65% of occupied homes are lived in by their owner (Maryland: 67%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Montgomery County | Maryland |
|---|---|---|
| Housing units | 405,127 | 2,545,532 |
| Detached houses | 47% | 51% |
| In buildings of 5 or more | 33% | 23% |
| Mobile homes | under 1% | 1% |
| Built before 1960 | 20% | 27% |
| Built since 2000 | 20% | 20% |
| Middle year built | 1980 | 1979 |
| Owner-occupied | 65% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.