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Radon Levels in Harford County, Maryland

EPA puts Harford County in Zone 1, its highest radon zone, and 22.6% of its 5,283 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

    22.6%

    1.3 pts below MD

    Harford
    22.6%
    Maryland
    23.9%

    5,283 tests, 2008 to 2017

  • Median result

    1.7pCi/L

    Below action level

    Harford
    1.7 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    5,283

    3rd of 19 by tests

    Harford
    5,283
    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

    11 of 19

    Middle half

    Harford
    22.6%
    Washington
    56.0%

    By share, of 19 with 30+ tests

Read a result for Harford County

Starts at Harford County's median, 1.7 pCi/L

1.7pCi/L

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

EPA’s reading of 1.7 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. Harford County's median reported result, 2008 to 2017.

Interpret this reading

The data

Harford County, At a glance

Harford County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Harford 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 70% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Harford County, 2008 to 2017, laboratory
Under 2 pCi/L: 54%2 to 4 pCi/L: 23%4 pCi/L and above: 23%

Of 5,283 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Harford County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L2,84653.9%
2 to 4 pCi/L1,24223.5%
4 pCi/L and above1,19522.6%
What these figures count

These are the 5,283 tests reported to CDC for Harford 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

Harford County, Compared

Harford County radon figures, compared

Calculated by Radon411

Harford County's 5,283 reported tests over the 2008 to 2017 laboratory totals had a middle value of 1.7 pCi/L and a maximum of 147.6 pCi/L, and 22.6% reached 4 pCi/L. Maryland as a whole (24 Maryland counties, pooled) comes to 23.9%: 1.3 points higher than here.

Among its state's counties it ranks 11th 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, 2,846 tests (53.9%) came in under 2 pCi/L, against 56.6% statewide, and 1,242 tests (23.5%) fell between 2 and 4, against 19.5% statewide. CDC's ten-year totals for Harford County went from 4,181 tests (2005 to 2014) to 5,283 (2008 to 2017), the share going from 21.1% to 22.6%.

EPA's 1993 zone map puts Harford County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 70% of the county's land high radon potential.

Next door, the shares run from 19.1% in Baltimore County to 59.7% in York County, PA, with Baltimore County below Harford County.

CDC also counts 812 tests taken after mitigation in Harford County for the same period: tests in homes where a fix was already in.

Harford County against Maryland, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Harford County
Harford County5,28322.6%1.7 pCi/LThis county
Maryland, pooled24 counties, pooled47,94123.9%Not pooled+1.3 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+13.1 points
Washington Countyhighest in the state1,25956.0%5.2 pCi/L+33.4 points
Wicomico Countylowest in the state320.0%0.9 pCi/L−22.6 points
York County, PAborders it8,78559.7%5.4 pCi/L+37.1 points
Lancaster County, PAborders it11,19455.1%4.8 pCi/L+32.5 points
Cecil County, MDborders it1,07124.9%1.9 pCi/L+2.3 points
Baltimore County, MDborders it7,70619.1%1.4 pCi/L−3.5 points
Where Harford County's reported results fell, 2008 to 2017, laboratory, beside Maryland and the United States
ResultHarford County testsHarford County shareMaryland shareU.S. shareAgainst Maryland
Under 2 pCi/L2,84653.9%56.6%39.6%−2.7 points
2 to 4 pCi/L1,24223.5%19.5%24.7%+4.0 points
4 pCi/L and above1,19522.6%23.9%35.7%−1.3 points
Harford 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
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
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
Harford County ten-year laboratory totals, against Maryland's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMaryland, pooledChange from the row before
2008 to 20175,28322.6%1.7 pCi/L147.6 pCi/L23.9%+0.4 points
2007 to 20164,96822.2%1.7 pCi/L147.6 pCi/L24.4%−0.3 points
2006 to 20154,48522.5%1.7 pCi/L147.6 pCi/L24.9%+1.4 points
2005 to 20144,18121.1%1.6 pCi/L146.2 pCi/L24.6%First on file

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

Harford County, Geology

The ground under Harford County

Predicted

USGS's geologic map splits Harford County: 70.2% of its land is high radon potential and 26.7% moderate. The map puts 70.2% of Harford County in the area it calls Eastern Piedmont and 26.7% 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 Harford County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Eastern PiedmontPrecambrian igneous and metamorphic rocks (schist and gneiss).High1270.2%
Western ShoreCretaceous, Quaternary, minor Tertiary gravel, sand, silt, clay.Moderate1026.7%

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

Harford County beside the ground around it

Harford County has more high-potential ground than Maryland as a whole: 70.2% of its land against 36.7%. Of the 4 counties that border it, 3 have more high-potential ground, Lancaster County, PA the most at 100%.

Share of land by USGS radon potential: Harford County, the 4 counties bordering it and Maryland
AreaEPA zoneLow potentialModerate potentialHigh potential
Harford CountyZone 1None26.7%70.2%
Baltimore CountyZone 1None16.1%81.1%
Cecil CountyZone 220.0%35.4%38.0%
Lancaster County, PAZone 1NoneNone100%
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

Harford County, Local resources

Radon testing and mitigation in Harford County

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

What it means

Harford County, Questions

Questions about radon in Harford County

Are radon levels high in Harford County?

Over the 2008 to 2017 laboratory totals, 22.6% of the radon tests reported to CDC for Harford County, Maryland were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.7 pCi/L. Of 19 Maryland counties with 30 or more tests for the same period, 10 reported a higher share; pooled, the state comes to 23.9%.

Which counties border Harford County?

Harford County borders 4 counties: Baltimore County, MD, Cecil County, MD, Lancaster County, PA and York County, PA.

Products

Harford County, Products

Testing a home in Harford County

In Harford County, 22.6% of 5,283 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 Harford 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

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

Explore

Harford County, Bordering counties

Counties bordering Harford County

Calculated by Radon411

Harford County, Cities and towns

Cities and towns in Harford County

The Census Bureau estimates 266,446 residents in Harford County for July 1, 2025, 5,211 more than in 2020 (+2.0%). That works out to 610 people per square mile of land. No town dominates: Aberdeen, the largest, has 18,374 residents, 6.9% of the total. Together its 3 incorporated places hold 16.7% of those residents; the other 83.3% live outside any of them. Testing is reported here more often than across the state: CDC's 5,283 reported tests for 2008 to 2017 come to 19.8 for every 1,000 residents (2025 estimate), against 7.7 for Maryland.

From Aberdeen to Bel Air, CDC publishes no figure by town: each reads Harford County's.

The cities and towns in Harford County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Aberdeen18,374+12.8%6.9%
Havre de Grace15,630+5.3%5.9%
Bel Air10,507−1.7%3.9%

3 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).

Harford County, Homes

Homes in Harford County

Of Harford County's 104,409 homes, 60% are detached houses, against 51% across Maryland; 14% are in buildings of five or more homes. Half of its homes were built before 1986, close to Maryland's 1979: 13% date from before 1960 and 24% from 2000 or later. Owners live in 80% of the occupied homes (Maryland: 67%), so for most households a test and a fix are their own to order.

Homes in Harford County, Maryland, 2019 to 2023
HomesHarford CountyMaryland
Housing units104,4092,545,532
Detached houses60%51%
In buildings of 5 or more14%23%
Mobile homes3%1%
Built before 196013%27%
Built since 200024%20%
Middle year built19861979
Owner-occupied80%67%

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