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Radon Levels in Washington County, Maryland

EPA puts Washington County in Zone 1, its highest radon zone, and high results are common there: 56.0% of the 1,259 radon tests reported to CDC (2008 to 2017, laboratory totals) came back 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

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  • Share at 4+ pCi/L

    56.0%

    32.1 pts above MD

    Washington
    56.0%
    Maryland
    23.9%

    1,259 tests, 2008 to 2017

  • Median result

    5.2pCi/L

    Action level reached

    Washington
    5.2 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    1,259

    9th of 19 by tests

    Washington
    1,259
    Montgomery
    10,969

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 1

    Highest potential

    1. Zone 1
    2. 2
    3. 3

    1 highest, 3 lowest

    EPA predicts over 4 pCi/L indoors

  • Rank in Maryland

    1 of 19

    Top quarter

    Washington
    56.0%
    Washington
    56.0%

    By share, of 19 with 30+ tests

Read a result for Washington County

Starts at Washington County's median, 5.2 pCi/L

5.2pCi/L

EPA’s own thresholds; the figures are the area’s, never this home’s.

EPA’s reading of 5.2 pCi/L

At or above 4 pCi/L

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 4 and aboveEPA says fix it

This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Washington County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Washington County, At a glance

Washington County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Washington County in and predicts an average indoor of greater than 4 pCi/L (greater than 150 Bq/m³) across the county. That is one forecast for the whole county, not a reading of any address in it; homes above EPA's turn up in all three zones.

USGS geologic potential: High across 96% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Washington County, 2008 to 2017, laboratory

Reported results by concentration band, Washington County, 2008 to 2017, laboratory
Under 2 pCi/L: 28%2 to 4 pCi/L: 16%4 pCi/L and above: 56%

Of 1,259 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Washington County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L35027.8%
2 to 4 pCi/L20416.2%
4 pCi/L and above70556.0%
What these figures count

These are the 1,259 tests reported to CDC for Washington 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).

How to read these figures

Washington County, Compared

Washington County radon figures, compared

Calculated by Radon411

More than half: 56.0% of the 1,259 radon tests reported to CDC for Washington County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 1st of 19 Maryland counties with 30 or more tests for the same period. That is 32.1 points above the 23.9% pooled from 24 Maryland counties.

The median result, 5.2 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 413.3 pCi/L. The rest split 27.8% under 2 pCi/L and 16.2% from 2 to 4 (Maryland: 56.6% and 19.5%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 56.0% share point the same way here.

3 of its 8 bordering counties with figures ran higher, led by Fulton County, PA at 69.7%; Loudoun County, VA reported 27.4%. Statewide for the same period, Kent County reported the highest share (52.6%) and Wicomico County the lowest (0.0%).

CDC's ten-year totals for Washington County went from 1,112 tests (2005 to 2014) to 1,259 (2008 to 2017), the share going from 59.7% to 56.0%.

Nationally, every county with a figure for the same period pools to 35.7%; Washington County sits 20.3 points above it. CDC also counts 76 tests taken after mitigation in Washington County for the same period: tests in homes where a fix was already in.

Washington County against Maryland, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Washington County
Washington County1,25956.0%5.2 pCi/LThis county
Maryland, pooled24 counties, pooled47,94123.9%Not pooled−32.1 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−20.3 points
Kent Countyhighest in the state5752.6%4.4 pCi/L−3.4 points
Wicomico Countylowest in the state320.0%0.9 pCi/L−56.0 points
Fulton County, PAborders it13269.7%7.9 pCi/L+13.7 points
Franklin County, PAborders it3,73463.6%6.0 pCi/L+7.6 points
Morgan County, WVborders it24158.1%5.8 pCi/L+2.1 points
Jefferson County, WVborders it89853.2%4.4 pCi/L−2.8 points
Berkeley County, WVborders it2,88850.7%4.0 pCi/L−5.3 points
Allegany County, MDborders it28635.7%2.7 pCi/L−20.3 points
Frederick County, MDborders it3,93328.1%1.5 pCi/L−27.9 points
Loudoun County, VAborders it4,45727.4%1.8 pCi/L−28.6 points
Where Washington County's reported results fell, 2008 to 2017, laboratory, beside Maryland and the United States
ResultWashington County testsWashington County shareMaryland shareU.S. shareAgainst Maryland
Under 2 pCi/L35027.8%56.6%39.6%−28.8 points
2 to 4 pCi/L20416.2%19.5%24.7%−3.3 points
4 pCi/L and above70556.0%23.9%35.7%+32.1 points
Washington County ranked among the 19 Maryland counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Washington County1 of 191,25956.0%5.2 pCi/L
Kent County2 of 195752.6%4.4 pCi/L
Carroll County3 of 193,33441.9%2.8 pCi/L
Garrett County4 of 1918737.4%3.0 pCi/L
Allegany County5 of 1928635.7%2.7 pCi/L
Howard County6 of 194,54930.8%2.0 pCi/L
Calvert County7 of 191,20530.2%2.0 pCi/L
Frederick County8 of 193,93328.1%1.5 pCi/L
Cecil County9 of 191,07124.9%1.9 pCi/L
Charles County10 of 1947724.1%1.8 pCi/L
Harford County11 of 195,28322.6%1.7 pCi/L
Washington County ten-year laboratory totals, against Maryland's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMaryland, pooledChange from the row before
2008 to 20171,25956.0%5.2 pCi/L413.3 pCi/L23.9%−0.5 points
2007 to 20161,27356.5%5.3 pCi/L413.3 pCi/L24.4%−2.3 points
2006 to 20151,23158.8%5.7 pCi/L413.3 pCi/L24.9%−0.9 points
2005 to 20141,11259.7%5.9 pCi/L238.1 pCi/L24.6%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period.

Washington County, Geology

The ground under Washington County

Predicted

Most of the ground under Washington County is one class on USGS's geologic map: 95.6% of its land is high radon potential, with 4.4% low. The map puts 70.7% of Washington County in the area it calls Great Valley and 23.8% in Valley and Ridge, with 2 smaller areas beside them. USGS gives both a radon index of 13, in the high band (12 to 17).

USGS's geologic areas under Washington County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Great ValleyCambrian-Ordovician carbonate and clastic sedimentary rocks.High1370.7%
Valley and RidgeSilurian and Devonian sandstone, siltstone, shale.High1323.8%
Blue RidgeCambrian-Precambrian igneous, metamorphic, and sedimentary rocks.Low84.4%
Northern Appalachian Valley and RidgeSandstone ridges, shale and limestone valleys, mostly DevonianHigh141.1%

Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.

Washington County beside the ground around it

Washington County has more high-potential ground than Maryland as a whole: 95.6% of its land against 36.7%. Of the 8 counties that border it, 4 have more high-potential ground, Fulton County, PA the most at 100%.

Share of land by USGS radon potential: Washington County, the 8 counties bordering it and Maryland
AreaEPA zoneLow potentialModerate potentialHigh potential
Washington CountyZone 14.4%None95.6%
Jefferson County, WVZone 1None4.3%95.7%
Berkeley County, WVZone 1NoneNone100%
Frederick CountyZone 133.5%19.1%47.4%
Loudoun County, VAZone 2None98.7%1.3%
Morgan County, WVZone 1NoneNone100%
Fulton County, PAZone 1NoneNone100%
Franklin County, PAZone 16.2%None93.8%
Allegany CountyZone 2None19.5%80.5%
Maryland24 counties, pooled by land areaVaries29.9%27.6%36.7%

The map rates the ground, not the air in any home.

Local help

Washington County, Local resources

Radon testing and mitigation in Washington County

Listed radon businesses with an address in Washington County:

Listed radon professionals by town: Boonsboro, Williamsport

What Maryland's program says
Phone
1-866-703-3266

What it means

Washington County, Questions

Questions about radon in Washington County

Are radon levels high in Washington County?

Over the 2008 to 2017 laboratory totals, 56.0% of the radon tests reported to CDC for Washington County, Maryland were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.2 pCi/L. Of 19 Maryland counties with 30 or more tests for the same period, none reported a higher share; pooled, the state comes to 23.9%.

Which counties border Washington County?

Washington County borders 8 counties: Jefferson County, WV, Berkeley County, WV, Frederick County, MD, Loudoun County, VA, Morgan County, WV, Fulton County, PA, Franklin County, PA and Allegany County, MD.

Products

Washington County, Products

Testing a home in Washington County

In Washington County, 56.0% of 1,259 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 Washington 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

Washington County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Washington County

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Washington County, Bordering counties

Counties bordering Washington County

Calculated by Radon411

Washington County, Cities and towns

Cities and towns in Washington County

The Census Bureau estimates 157,731 residents in Washington County for July 1, 2025, 3,032 more than in 2020 (+2.0%). That works out to 345 people per square mile of land. Its largest town, Hagerstown, has 44,228 residents, 28.0% of the total. Together its 9 incorporated places hold 36.8% of those residents; the other 63.2% live outside any of them. CDC's 1,259 reported tests for 2008 to 2017 work out to 8.0 per 1,000 residents (2025 estimate), close to Maryland's 7.7.

From Hagerstown to Clear Spring, CDC publishes no figure by town: each reads Washington County's.

The cities and towns in Washington County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Hagerstown44,228+1.6%28.0%
Boonsboro3,867+2.0%2.5%
Smithsburg3,212+7.4%2.0%
Williamsport2,112+1.4%1.3%
Hancock1,581+2.2%1.0%
Keedysville1,225+2.3%0.8%
Funkstown863+1.9%0.5%
Sharpsburg573+2.5%0.4%
Clear Spring378+1.9%0.2%

9 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).

Washington County, Homes

Homes in Washington County

Of Washington County's 63,965 homes, 62% are detached houses, against 51% across Maryland; 14% are in buildings of five or more homes. Half of its homes were built before 1974, close to Maryland's 1979: 35% date from before 1960 and 19% from 2000 or later. 66% 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 in Washington County, Maryland, 2019 to 2023
HomesWashington CountyMaryland
Housing units63,9652,545,532
Detached houses62%51%
In buildings of 5 or more14%23%
Mobile homes2%1%
Built before 196035%27%
Built since 200019%20%
Middle year built19741979
Owner-occupied66%67%

Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.