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Radon Levels in Baltimore County, Maryland

EPA puts Baltimore County in Zone 1, its highest radon zone, and 19.1% of its 7,706 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

    19.1%

    4.8 pts below MD

    Baltimore
    19.1%
    Maryland
    23.9%

    7,706 tests, 2008 to 2017

  • Median result

    1.4pCi/L

    Below action level

    Baltimore
    1.4 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    7,706

    2nd of 19 by tests

    Baltimore
    7,706
    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

    13 of 19

    Middle half

    Baltimore
    19.1%
    Washington
    56.0%

    By share, of 19 with 30+ tests

Read a result for Baltimore County

Starts at Baltimore County's median, 1.4 pCi/L

1.4pCi/L

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

EPA’s reading of 1.4 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. Baltimore County's median reported result, 2008 to 2017.

Interpret this reading

The data

Baltimore County, At a glance

Baltimore County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Baltimore 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 81% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Baltimore County, 2008 to 2017, laboratory
Under 2 pCi/L: 62%2 to 4 pCi/L: 19%4 pCi/L and above: 19%

Of 7,706 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Baltimore County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L4,73861.5%
2 to 4 pCi/L1,49719.4%
4 pCi/L and above1,47119.1%
What these figures count

These are the 7,706 tests reported to CDC for Baltimore 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

Baltimore County, Compared

Baltimore County radon figures, compared

Calculated by Radon411

Baltimore County's 7,706 reported tests over the 2008 to 2017 laboratory totals had a middle value of 1.4 pCi/L and a maximum of 226.4 pCi/L, and 19.1% reached 4 pCi/L. Maryland as a whole (24 Maryland counties, pooled) comes to 23.9%: 4.8 points higher than here.

Among its state's counties it ranks 13th 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, 4,738 tests (61.5%) came in under 2 pCi/L, against 56.6% statewide, and 1,497 tests (19.4%) fell between 2 and 4, against 19.5% statewide. CDC's ten-year totals for Baltimore County went from 5,459 tests (2005 to 2014) to 7,706 (2008 to 2017), the share going from 21.0% to 19.1%.

EPA's 1993 zone map puts Baltimore County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 81% of the county's land high radon potential.

Next door, the shares run from 7.9% in Baltimore city to 59.7% in York County, PA, with Anne Arundel County and Baltimore city below Baltimore County.

CDC also counts 977 tests taken after mitigation in Baltimore County for the same period: tests in homes where a fix was already in.

Baltimore County against Maryland, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Baltimore County
Baltimore County7,70619.1%1.4 pCi/LThis county
Maryland, pooled24 counties, pooled47,94123.9%Not pooled+4.8 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+16.6 points
Washington Countyhighest in the state1,25956.0%5.2 pCi/L+36.9 points
Wicomico Countylowest in the state320.0%0.9 pCi/L−19.1 points
York County, PAborders it8,78559.7%5.4 pCi/L+40.6 points
Carroll County, MDborders it3,33441.9%2.8 pCi/L+22.8 points
Howard County, MDborders it4,54930.8%2.0 pCi/L+11.7 points
Harford County, MDborders it5,28322.6%1.7 pCi/L+3.5 points
Anne Arundel County, MDborders it4,08817.4%1.4 pCi/L−1.7 points
Baltimore city, MDborders it1,1487.9%0.8 pCi/L−11.2 points
Where Baltimore County's reported results fell, 2008 to 2017, laboratory, beside Maryland and the United States
ResultBaltimore County testsBaltimore County shareMaryland shareU.S. shareAgainst Maryland
Under 2 pCi/L4,73861.5%56.6%39.6%+4.9 points
2 to 4 pCi/L1,49719.4%19.5%24.7%−0.1 points
4 pCi/L and above1,47119.1%23.9%35.7%−4.8 points
Baltimore 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
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
Prince George's County14 of 191,60319.0%1.4 pCi/L
Montgomery County15 of 1910,96918.0%1.3 pCi/L
Anne Arundel County16 of 194,08817.4%1.4 pCi/L
Queen Anne's County17 of 196516.9%1.3 pCi/L
Baltimore city18 of 191,1487.9%0.8 pCi/L
Baltimore County ten-year laboratory totals, against Maryland's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMaryland, pooledChange from the row before
2008 to 20177,70619.1%1.4 pCi/L226.4 pCi/L23.9%−0.8 points
2007 to 20166,99019.9%1.5 pCi/L226.4 pCi/L24.4%−1.3 points
2006 to 20155,99121.2%1.5 pCi/L226.4 pCi/L24.9%+0.2 points
2005 to 20145,45921.0%1.5 pCi/L226.4 pCi/L24.6%First on file

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

Baltimore County, Geology

The ground under Baltimore County

Predicted

Most of the ground under Baltimore County is one class on USGS's geologic map: 81.1% of its land is high radon potential, with 16.1% moderate. The map puts 81.1% of Baltimore County in the area it calls Eastern Piedmont and 16.1% in Western Shore. USGS gives the first a radon index of 12, in the high band (12 to 17), and the second 10, in the moderate band (9 to 11).

USGS's geologic areas under Baltimore County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Eastern PiedmontPrecambrian igneous and metamorphic rocks (schist and gneiss).High1281.1%
Western ShoreCretaceous, Quaternary, minor Tertiary gravel, sand, silt, clay.Moderate1016.1%

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

Baltimore County beside the ground around it

Baltimore County has more high-potential ground than Maryland as a whole: 81.1% of its land against 36.7%. Of the 6 counties that border it, 3 have more high-potential ground, York County, PA the most at 99.2%.

Share of land by USGS radon potential: Baltimore County, the 6 counties bordering it and Maryland
AreaEPA zoneLow potentialModerate potentialHigh potential
Baltimore CountyZone 1None16.1%81.1%
Baltimore cityZone 2None55.3%36.7%
Harford CountyZone 1None26.7%70.2%
Carroll CountyZone 1None14.3%85.7%
Howard CountyZone 1None8.8%91.2%
Anne Arundel CountyZone 2None56.8%34.1%
York County, PAZone 10.7%None99.2%
Maryland24 counties, pooled by land areaVaries29.9%27.6%36.7%

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

Local help

Baltimore County, Local resources

Radon testing and mitigation in Baltimore County

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

What it means

Baltimore County, Questions

Questions about radon in Baltimore County

Are radon levels high in Baltimore County?

Over the 2008 to 2017 laboratory totals, 19.1% of the radon tests reported to CDC for Baltimore County, Maryland were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.4 pCi/L. Of 19 Maryland counties with 30 or more tests for the same period, 12 reported a higher share; pooled, the state comes to 23.9%.

Which counties border Baltimore County?

Baltimore County borders 6 counties: Baltimore city, MD, Harford County, MD, Carroll County, MD, Howard County, MD, Anne Arundel County, MD and York County, PA.

Products

Baltimore County, Products

Testing a home in Baltimore County

In Baltimore County, 19.1% of 7,706 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 Baltimore 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

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

Explore

Baltimore County, Bordering counties

Counties bordering Baltimore County

Calculated by Radon411

Baltimore County, Residents

Who lives in Baltimore County

About 847,650 people live in Baltimore County by the Census Bureau's estimate for July 1, 2025, 5,700 fewer than in 2020 (−0.7%). Packed into its land, that is 1,417 people per square mile. CDC's 7,706 reported tests for 2008 to 2017 work out to 9.1 per 1,000 residents (2025 estimate), close to Maryland's 7.7.

Census lists no incorporated place in Baltimore County: every home in it reads the county's figures.

Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025).

Baltimore County, Homes

Homes in Baltimore County

Fewer than six in ten of Baltimore County's 350,296 homes are detached houses (47%, against 51% across Maryland); the rest are attached, in shared buildings or mobile. Half of its homes were built before 1973, close to Maryland's 1979: 33% date from before 1960 and 14% 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 Baltimore County, Maryland, 2019 to 2023
HomesBaltimore CountyMaryland
Housing units350,2962,545,532
Detached houses47%51%
In buildings of 5 or more25%23%
Mobile homes1%1%
Built before 196033%27%
Built since 200014%20%
Middle year built19731979
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.