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Radon Levels in Frederick County, Maryland

EPA puts Frederick County in Zone 1, its highest radon zone, and 28.1% of its 3,933 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

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  • Share at 4+ pCi/L

    28.1%

    4.2 pts above MD

    Frederick
    28.1%
    Maryland
    23.9%

    3,933 tests, 2008 to 2017

  • Median result

    1.5pCi/L

    Below action level

    Frederick
    1.5 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    3,933

    6th of 19 by tests

    Frederick
    3,933
    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

    8 of 19

    Middle half

    Frederick
    28.1%
    Washington
    56.0%

    By share, of 19 with 30+ tests

Read a result for Frederick County

Starts at Frederick County's median, 1.5 pCi/L

1.5pCi/L

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

EPA’s reading of 1.5 pCi/L

Below 2 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 below 2 pCi/L, the level at which EPA says a fix should be considered. Frederick County's median reported result, 2008 to 2017.

Interpret this reading

The data

Frederick County, At a glance

Frederick County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Frederick 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 47% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Frederick County, 2008 to 2017, laboratory
Under 2 pCi/L: 57%2 to 4 pCi/L: 15%4 pCi/L and above: 28%

Of 3,933 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Frederick County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L2,22056.4%
2 to 4 pCi/L60615.4%
4 pCi/L and above1,10728.1%
What these figures count

These are the 3,933 tests reported to CDC for Frederick 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

Frederick County, Compared

Frederick County radon figures, compared

Calculated by Radon411

Frederick County's 3,933 reported tests over the 2008 to 2017 laboratory totals had a middle value of 1.5 pCi/L and a maximum of 193.9 pCi/L, and 28.1% reached 4 pCi/L. Maryland as a whole (24 Maryland counties, pooled) comes to 23.9%: 4.2 points lower than here.

Among its state's counties it ranks 8th 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, 2,220 tests (56.4%) came in under 2 pCi/L, against 56.6% statewide, and 606 tests (15.4%) fell between 2 and 4, against 19.5% statewide. CDC's ten-year totals for Frederick County went from 2,982 tests (2005 to 2014) to 3,933 (2008 to 2017), the share going from 27.7% to 28.1%.

EPA's 1993 zone map puts Frederick County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 47% of the county's land high radon potential.

Next door, the shares run from 18.0% in Montgomery County to 63.6% in Franklin County, PA, with Loudoun County, VA and Montgomery County below Frederick County.

CDC also counts 156 tests taken after mitigation in Frederick County for the same period: tests in homes where a fix was already in.

Frederick County against Maryland, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Frederick County
Frederick County3,93328.1%1.5 pCi/LThis county
Maryland, pooled24 counties, pooled47,94123.9%Not pooled−4.2 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+7.6 points
Kent Countyhighest in the state5752.6%4.4 pCi/L+24.5 points
Wicomico Countylowest in the state320.0%0.9 pCi/L−28.1 points
Franklin County, PAborders it3,73463.6%6.0 pCi/L+35.5 points
Washington County, MDborders it1,25956.0%5.2 pCi/L+27.9 points
Adams County, PAborders it3,25246.4%3.6 pCi/L+18.3 points
Carroll County, MDborders it3,33441.9%2.8 pCi/L+13.8 points
Howard County, MDborders it4,54930.8%2.0 pCi/L+2.7 points
Loudoun County, VAborders it4,45727.4%1.8 pCi/L−0.7 points
Montgomery County, MDborders it10,96918.0%1.3 pCi/L−10.1 points
Where Frederick County's reported results fell, 2008 to 2017, laboratory, beside Maryland and the United States
ResultFrederick County testsFrederick County shareMaryland shareU.S. shareAgainst Maryland
Under 2 pCi/L2,22056.4%56.6%39.6%−0.2 points
2 to 4 pCi/L60615.4%19.5%24.7%−4.1 points
4 pCi/L and above1,10728.1%23.9%35.7%+4.2 points
Frederick 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
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
St. Mary's County12 of 1963620.9%1.8 pCi/L
Baltimore County13 of 197,70619.1%1.4 pCi/L
Frederick County ten-year laboratory totals, against Maryland's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMaryland, pooledChange from the row before
2008 to 20173,93328.1%1.5 pCi/L193.9 pCi/L23.9%−0.1 points
2007 to 20163,74728.2%1.5 pCi/L268.1 pCi/L24.4%+0.1 points
2006 to 20153,36128.1%1.5 pCi/L268.1 pCi/L24.9%+0.4 points
2005 to 20142,98227.7%1.4 pCi/L268.1 pCi/L24.6%First on file

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

Frederick County, Geology

The ground under Frederick County

Predicted

No class of ground holds half of Frederick County on USGS's geologic map: 47.4% of its land is high radon potential, 19.1% moderate and 33.5% low. The map puts 33.5% of Frederick County in the area it calls Blue Ridge and 30.2% in Western Piedmont, with 4 smaller areas beside them. USGS gives the first a radon index of 8, in the low band (5 to 8), and the second 15, in the high band (12 to 17).

USGS's geologic areas under Frederick County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Blue RidgeCambrian-Precambrian igneous, metamorphic, and sedimentary rocks.Low833.5%
Western PiedmontPrecambrian phyllitic metamorphic rocks.High1530.2%
Frederick ValleyCambrian-Ordovician carbonate and clastic sedimentary rocks.High1316.4%
Mesozoic BasinsTriassic-Jurassic sedimentary and igneous rocks.Moderate1115.0%
Mesozoic BasinsTriassic-Jurassic shale, sandstone, conglomerate, and intrusive igneous rocks.Moderate113.7%
Eastern PiedmontPrecambrian igneous and metamorphic rocks (schist and gneiss).High120.8%

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

Frederick County beside the ground around it

Frederick County has more high-potential ground than Maryland as a whole: 47.4% of its land against 36.7%. Of the 7 counties that border it, 6 have more high-potential ground, Washington County the most at 95.6%.

Share of land by USGS radon potential: Frederick County, the 7 counties bordering it and Maryland
AreaEPA zoneLow potentialModerate potentialHigh potential
Frederick CountyZone 133.5%19.1%47.4%
Washington CountyZone 14.4%None95.6%
Carroll CountyZone 1None14.3%85.7%
Montgomery CountyZone 1None19.8%80.2%
Adams County, PAZone 127.7%None72.3%
Howard CountyZone 1None8.8%91.2%
Loudoun County, VAZone 2None98.7%1.3%
Franklin County, PAZone 16.2%None93.8%
Maryland24 counties, pooled by land areaVaries29.9%27.6%36.7%

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

Local help

Frederick County, Local resources

Radon testing and mitigation in Frederick County

Listed radon businesses with an address in Frederick County:

Listed radon professionals by town: Emmitsburg

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

What it means

Frederick County, Questions

Questions about radon in Frederick County

Are radon levels high in Frederick County?

Over the 2008 to 2017 laboratory totals, 28.1% of the radon tests reported to CDC for Frederick County, Maryland were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.5 pCi/L. Of 19 Maryland counties with 30 or more tests for the same period, 7 reported a higher share; pooled, the state comes to 23.9%.

Which counties border Frederick County?

Frederick County borders 7 counties: Washington County, MD, Carroll County, MD, Montgomery County, MD, Adams County, PA, Howard County, MD, Loudoun County, VA and Franklin County, PA.

Products

Frederick County, Products

Testing a home in Frederick County

In Frederick County, 28.1% of 3,933 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 Frederick 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

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

Explore

Frederick County, Bordering counties

Counties bordering Frederick County

Calculated by Radon411

Frederick County, Cities and towns

Cities and towns in Frederick County

Frederick County is growing: the Census Bureau puts it at 302,883 residents on July 1, 2025, up 11.0% from 272,767 in 2020. That works out to 459 people per square mile of land. Its largest town, Frederick, has 92,059 residents, 30.4% of the total. Testing is reported here more often than across the state: CDC's 3,933 reported tests for 2008 to 2017 come to 13.0 for every 1,000 residents (2025 estimate), against 7.7 for Maryland.

From Frederick to Burkittsville, CDC publishes no figure by town: each reads Frederick County's.

The cities and towns in Frederick County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Frederick92,059+17.4%30.4%
Mount Airyextends beyond Frederick County9,857+2.2%Counted whole
Brunswick9,380+20.2%3.1%
Walkersville6,501+5.5%2.1%
Thurmont6,337+2.1%2.1%
Middletown5,056+2.2%1.7%
Emmitsburg2,910+5.2%1.0%
Myersville1,885+4.4%0.6%
New Market1,609+5.6%0.5%
Woodsboro1,136+4.3%0.4%
Rosemont258+1.2%Under 0.1%
Burkittsville145+2.1%Under 0.1%

12 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). A place that extends beyond Frederick County is counted whole, so it has no share.

Frederick County, Homes

Homes in Frederick County

Of Frederick County's 106,480 homes, 60% are detached houses, against 51% across Maryland; 14% are in buildings of five or more homes. Much of Frederick County is recent building: 31% of its homes have gone up since 2000 and the middle year built is 1990, against 1979 for Maryland. Owners live in 77% of the occupied homes (Maryland: 67%), so for most households a test and a fix are their own to order.

Homes in Frederick County, Maryland, 2019 to 2023
HomesFrederick CountyMaryland
Housing units106,4802,545,532
Detached houses60%51%
In buildings of 5 or more14%23%
Mobile homes1%1%
Built before 196018%27%
Built since 200031%20%
Middle year built19901979
Owner-occupied77%67%

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