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Radon Levels in Delaware County, Pennsylvania

EPA puts Delaware County in Zone 1, its highest radon zone, and most reported tests there come back low, though 14.7% of 6,041 (2020) reached 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    14.7%

    15.6 pts below PA

    Delaware
    14.7%
    PA
    30.3%

    6,041 tests, 2020

  • Median result

    1.8pCi/L

    Below action level

    Delaware
    1.8 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2020

  • Tests reported

    6,041

    6th of 63 by tests

    Delaware
    6,041
    Montgomery
    10,508

    Reported to CDC before any fix, 2020

  • 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 PA

    62 of 63

    Lowest quarter

    Delaware
    14.7%
    Perry
    57.7%

    By share, of 63 with 30+ tests

Read a result for Delaware County

Starts at Delaware County's median, 1.8 pCi/L

1.8pCi/L

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

EPA’s reading of 1.8 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. Delaware County's median reported result, 2020.

Interpret this reading

The data

Delaware County, At a glance

Delaware County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Delaware 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 77% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Delaware County, 2020

Share of reported tests at or above 4 pCi/L, by year, Delaware County
Share of reported tests at or above 4 pCi/L, by year, Delaware County
YearShare of reported tests at or above 4 pCi/L
201419.4%
201520.7%
201617.0%
201717.0%
201816.2%
201915.3%
202014.7%

2020: 14.7%. Across these years the share ran from 14.7% to 20.7%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 6,041 tests reported to CDC for Delaware County over 2020, 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: 2020. Measured data period: 2005 to 2020 (every CDC figure on file).

How to read these figures

Delaware County, Compared

Delaware County radon figures, compared

Calculated by Radon411

Delaware County reports fewer high tests than Pennsylvania overall. 14.7% of its 6,041 tests in 2020 were at or above 4 pCi/L. That is 15.6 points below the 30.3% pooled from 67 Pennsylvania counties.

Ordered from highest share down, it comes 62nd of 63 Pennsylvania counties with 30 or more tests for the same period. Nationally, every county with a figure for the same period pools to 25.5%; Delaware County sits 10.8 points below it.

Next door, the shares run from 10.6% in Philadelphia County to 24.0% in Chester County, with Gloucester County, NJ and Philadelphia County below Delaware County. The reported tests do not follow EPA's Zone 1 label for Delaware County (predicted average above 4 pCi/L): 14.7% of them reached 4 pCi/L, fewer than that label suggests.

Half the tests came in under 1.8 pCi/L and half over it; the single highest reached 65.1 pCi/L. The rest split 53.3% under 2 pCi/L and 31.9% from 2 to 4 (Pennsylvania: 44.3% and 25.4%). Year by year, 2014 opened at 19.4% and 2020 closed at 14.7% (down 4.7 points), with 2015 the high at 20.7%.

The busiest year on file was 2020, with 6,041 tests reported; the quietest, 2014, had 4,171.

Share of reported tests at or above 4 pCi/L by year, Delaware County against Pennsylvania2014 to 2020, years with 30 or more tests: Delaware County 19.4% to 14.7%, the state's pooled share 30.3% in 2020.
Delaware CountyPennsylvania, pooled
Share of reported tests at or above 4 pCi/L by year, Delaware County against Pennsylvania: data table
YearTestsDelaware County, at or above 4 pCi/LPennsylvania, pooled
20144,17119.4%36.1%
20154,62820.7%37.8%
20165,24717.0%34.4%
20175,29617.0%35.1%
20185,56616.2%30.5%
20195,82815.3%31.4%
20206,04114.7%30.3%
Delaware County against Pennsylvania, the United States and nearby counties, 2020
AreaTestsAt or above 4 pCi/LMedianDifference from Delaware County
Delaware County6,04114.7%1.8 pCi/LThis county
Pennsylvania, pooled67 counties, pooled93,66930.3%Not pooled+15.6 points
United States, pooled915 counties, pooled405,35525.5%Not pooled+10.8 points
Perry Countyhighest in the state18957.7%4.9 pCi/L+43.0 points
Fayette Countylowest in the state28717.4%1.8 pCi/L+2.7 points
Chester County, PAborders it6,77024.0%2.0 pCi/L+9.3 points
Montgomery County, PAborders it10,50821.8%2.0 pCi/L+7.1 points
Gloucester County, NJborders it4,45313.5%1.2 pCi/L−1.2 points
Philadelphia County, PAborders it8,44210.6%1.7 pCi/L−4.1 points
Where Delaware County's reported results fell, 2020, beside Pennsylvania and the United States
ResultDelaware County testsDelaware County sharePennsylvania shareU.S. shareAgainst Pennsylvania
Under 2 pCi/L3,22253.3%44.3%51.6%+9.0 points
2 to 4 pCi/L1,93031.9%25.4%22.9%+6.5 points
4 pCi/L and above88914.7%30.3%25.5%−15.6 points
Delaware County ranked among the 63 Pennsylvania counties with 30 or more tests, by share at or above 4 pCi/L, 2020
CountyRankTestsAt or above 4 pCi/LMedian
Luzerne County53 of 6399128.2%2.0 pCi/L
Lackawanna County54 of 6377627.1%2.1 pCi/L
Chester County55 of 636,77024.0%2.0 pCi/L
Bucks County56 of 637,06623.2%2.0 pCi/L
Erie County57 of 631,16222.2%1.9 pCi/L
Montgomery County58 of 6310,50821.8%2.0 pCi/L
Greene County59 of 634520.0%3.2 pCi/L
Potter County60 of 6319517.9%1.1 pCi/L
Fayette County61 of 6328717.4%1.8 pCi/L
Delaware County62 of 636,04114.7%1.8 pCi/L
Philadelphia County63 of 638,44210.6%1.7 pCi/L
Delaware County radon tests by year, against Pennsylvania's pooled share
YearTestsAt or above 4 pCi/LMedianHighestPennsylvania, pooledChange from the row before
20206,04114.7%1.8 pCi/L65.1 pCi/L30.3%−0.6 points
20195,82815.3%1.8 pCi/L125.0 pCi/L31.4%−0.9 points
20185,56616.2%1.8 pCi/L105.1 pCi/L30.5%−0.8 points
20175,29617.0%1.8 pCi/L85.9 pCi/L35.1%Level
20165,24717.0%1.9 pCi/L62.9 pCi/L34.4%−3.7 points
20154,62820.7%2.0 pCi/L125.6 pCi/L37.8%+1.3 points
20144,17119.4%1.9 pCi/L98.3 pCi/L36.1%First on file

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

Delaware County, State data

Pennsylvania's own radon test data

Measured

What Pennsylvania's own agencies publish about radon tests in Delaware County, with their period. These are not CDC's figures and are never added to them.

MeasuredState figures, not CDC's

What Pennsylvania DEP reports for the ZIP codes in Delaware County

Pennsylvania DEP publishes its figures by ZIP code, not by county. These are the 45 ZIP codes that lie wholly or partly in Delaware County, each with the state's own figures for it. Period: Period not stated by DEP.

ZIP codes in Delaware County
ZIP codeWhat the state reports
19003Basement: average 2.5 pCi/L, 3,078 tests; First floor: average 1.3 pCi/L, 723 tests
19008Basement: average 3.4 pCi/L, 3,658 tests; First floor: average 2.0 pCi/L, 714 tests
19010Basement: average 3.2 pCi/L, 4,858 tests; First floor: average 1.7 pCi/L, 1,151 tests
19013Basement: average 1.8 pCi/L, 814 tests; First floor: average 0.9 pCi/L, 165 tests
19014Basement: average 2.3 pCi/L, 2,998 tests; First floor: average 1.2 pCi/L, 383 tests
19015Basement: average 1.6 pCi/L, 1,460 tests; First floor: average 1.0 pCi/L, 233 tests
19017Basement: average 2.4 pCi/L, 57 tests; First floor: figures not shown
19018Basement: average 2.3 pCi/L, 2,340 tests; First floor: average 1.3 pCi/L, 418 tests
19022Basement: average 1.3 pCi/L, 160 tests; First floor: figures not shown
19023Basement: average 1.5 pCi/L, 967 tests; First floor: average 1.0 pCi/L, 197 tests
19026Basement: average 2.7 pCi/L, 5,518 tests; First floor: average 1.7 pCi/L, 1,002 tests
19029Basement: average 1.4 pCi/L, 171 tests; First floor: average 0.9 pCi/L, 34 tests
19032Basement: average 1.2 pCi/L, 646 tests; First floor: average 1.0 pCi/L, 49 tests
19033Basement: average 2.1 pCi/L, 799 tests; First floor: average 1.1 pCi/L, 113 tests
19036Basement: average 1.6 pCi/L, 1,200 tests; First floor: average 1.2 pCi/L, 168 tests
19041Basement: average 3.9 pCi/L, 1,595 tests; First floor: average 1.9 pCi/L, 348 tests
19043Basement: average 1.4 pCi/L, 212 tests; First floor: average 1.0 pCi/L, 48 tests
19050Basement: average 2.8 pCi/L, 3,542 tests; First floor: average 1.5 pCi/L, 835 tests
19052Basement: figures not shown; First floor: figures not shown
19060Basement: average 2.6 pCi/L, 871 tests; First floor: figures not shown
19061Basement: average 2.5 pCi/L, 2,384 tests; First floor: average 1.4 pCi/L, 375 tests
19063Basement: average 4.1 pCi/L, 8,556 tests; First floor: average 2.5 pCi/L, 1,260 tests
19064Basement: average 3.7 pCi/L, 5,237 tests; First floor: average 2.1 pCi/L, 821 tests
19070Basement: average 2.9 pCi/L, 839 tests; First floor: average 2.2 pCi/L, 115 tests
19073Basement: average 3.0 pCi/L, 4,853 tests; First floor: average 1.8 pCi/L, 871 tests
19074Basement: average 1.8 pCi/L, 438 tests; First floor: average 1.2 pCi/L, 83 tests
19076Basement: average 2.0 pCi/L, 479 tests; First floor: average 0.9 pCi/L, 94 tests
19078Basement: average 2.1 pCi/L, 1,205 tests; First floor: average 1.1 pCi/L, 184 tests
19079Basement: average 1.9 pCi/L, 607 tests; First floor: average 0.9 pCi/L, 82 tests
19081Basement: average 2.7 pCi/L, 1,739 tests; First floor: average 1.5 pCi/L, 306 tests
19082Basement: average 2.3 pCi/L, 2,841 tests; First floor: average 1.1 pCi/L, 694 tests
19083Basement: average 3.0 pCi/L, 8,162 tests; First floor: average 1.8 pCi/L, 1,294 tests
19085Basement: average 2.4 pCi/L, 1,955 tests; First floor: average 1.4 pCi/L, 464 tests
19086Basement: average 2.9 pCi/L, 2,853 tests; First floor: average 1.7 pCi/L, 514 tests
19087Basement: average 5.7 pCi/L, 12,385 tests; First floor: average 3.6 pCi/L, 2,801 tests
19094Basement: average 2.1 pCi/L, 416 tests; First floor: average 1.1 pCi/L, 52 tests
19096Basement: average 3.1 pCi/L, 4,474 tests; First floor: average 1.9 pCi/L, 960 tests
19113Basement: figures not shown
19153Basement: average 0.9 pCi/L, 259 tests; First floor: average 0.6 pCi/L, 62 tests
19312Basement: average 6.2 pCi/L, 5,455 tests; First floor: average 4.0 pCi/L, 1,193 tests
19317Basement: average 2.5 pCi/L, 2,878 tests; First floor: average 1.5 pCi/L, 421 tests
19319Basement: average 3.8 pCi/L, 50 tests; First floor: figures not shown
19342Basement: average 2.7 pCi/L, 3,277 tests; First floor: average 1.6 pCi/L, 509 tests
19373Basement: average 3.4 pCi/L, 632 tests; First floor: average 1.8 pCi/L, 109 tests
19382Basement: average 3.0 pCi/L, 13,002 tests; First floor: average 1.8 pCi/L, 2,090 tests
  • DEP's report gives the number of tests, the highest result and the average result for each floor tested; it states no period.
  • DEP says the smartest thing to do is to test your home for radon, no matter where you live.
  • A ZIP code that crosses the county line is listed whole; its figures cover all of it.

Measured: Pennsylvania DEP data, Period not stated by DEP.

Delaware County, Geology

The ground under Delaware County

Predicted

Most of the ground under Delaware County is one class on USGS's geologic map: 76.6% of its land is high radon potential, with 23.4% moderate. The map puts 76.6% of Delaware County in the area it calls Piedmont Lowland and 22.7% in Atlantic Coastal Plain. USGS gives the first a radon index of 14, in the high band (12 to 17), and the second 10, in the moderate band (9 to 11).

USGS's geologic areas under Delaware County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Piedmont LowlandMica schist, phyllite, hornblende gneiss, and marble.High1476.6%
Atlantic Coastal PlainGlacial deposits and marine sediments.Moderate1022.7%

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

Delaware County beside the ground around it

On high-potential ground Delaware County is close to Pennsylvania as a whole: 76.6% of its land against 70.4%. Of the 5 counties that border it, 2 have more high-potential ground, Montgomery County the most at 100%.

Share of land by USGS radon potential: Delaware County, the 5 counties bordering it and Pennsylvania
AreaEPA zoneLow potentialModerate potentialHigh potential
Delaware CountyZone 1None23.4%76.6%
Philadelphia CountyZone 3None63.6%36.5%
Chester CountyZone 1None0.1%99.9%
Gloucester County, NJZone 267.7%32.3%None
Montgomery CountyZone 1NoneNone100%
New Castle County, DEZone 235.7%63.8%None
Pennsylvania67 counties, pooled by land areaVaries0.7%28.9%70.4%

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

Local help

Delaware County, Local resources

Radon testing and mitigation in Delaware County

Listed radon businesses with an address in Delaware County:

Listed radon professionals by town: Brookhaven, Glenolden, Media

What Pennsylvania's program says
Phone
800-237-2366
Licensing of radon professionals
The Radon Certification Act requires DEP to establish by regulation, a certification program for persons conducting radon gas and radon progeny testing, laboratory analysis and mitigation of radon contamination in buildings.

What it means

Delaware County, Questions

Questions about radon in Delaware County

Are radon levels high in Delaware County?

In 2020, 14.7% of the radon tests reported to CDC for Delaware County, Pennsylvania were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.8 pCi/L. Of 63 Pennsylvania counties with 30 or more tests for the same period, 61 reported a higher share; pooled, the state comes to 30.3%.

Which counties border Delaware County?

Delaware County borders 5 counties: Philadelphia County, PA, Chester County, PA, Gloucester County, NJ, Montgomery County, PA and New Castle County, DE.

Products

Delaware County, Products

Testing a home in Delaware County

In Delaware County, 14.7% of 6,041 tests reported to CDC in 2020 reached 4 pCi/L, against 30.3% pooled across Pennsylvania. In Zone 1 the year-round level in Delaware 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

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

Explore

Delaware County, Bordering counties

Counties bordering Delaware County

Calculated by Radon411

Delaware County, Cities and towns

Cities and towns in Delaware County

The Census Bureau estimates 580,937 residents in Delaware County for July 1, 2025, 4,432 more than in 2020 (+0.8%). Packed into its land, that is 3,160 people per square mile. No town dominates: Chester, the largest, has 33,996 residents, 5.9% of the total. Together its 28 incorporated places hold 30.1% of those residents; the other 69.9% live outside any of them. CDC's 6,041 reported tests for 2020 work out to 10.4 per 1,000 residents (2025 estimate), close to Pennsylvania's 7.2.

From Chester to Rutledge, CDC publishes no figure by town: each reads Delaware County's.

The 12 largest cities and towns in Delaware County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Chester33,996+4.0%5.9%
Yeadon12,320+2.4%2.1%
Lansdowne11,141+0.5%1.9%
Darby10,666−0.2%1.8%
Collingdale8,898Level1.5%
Brookhaven8,362+0.8%1.4%
Ridley Park7,255Level1.2%
Glenolden7,217−0.1%1.2%
Clifton Heights6,835−0.1%1.2%
Folcroft6,780−0.1%1.2%
Swarthmore6,561+0.5%1.1%
Prospect Park6,409−0.2%1.1%
  • Sharon Hill
  • Norwood
  • Media
  • Aldan
  • Chester Heights
  • Upland
  • Morton
  • East Lansdowne
  • Colwyn
  • Eddystone
  • Marcus Hook
  • Parkside
  • Trainer
  • Millbourne
  • Rose Valley
  • Rutledge

28 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).

Delaware County, Homes

Homes in Delaware County

Fewer than six in ten of Delaware County's 229,390 homes are detached houses (44%, against 57% across Pennsylvania); the rest are attached, in shared buildings or mobile. The homes are older than Pennsylvania's as a whole: half were built before 1957 (1965 for Pennsylvania), and 58% date from before 1960. 70% of occupied homes are lived in by their owner (Pennsylvania: 69%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Delaware County, Pennsylvania, 2019 to 2023
HomesDelaware CountyPennsylvania
Housing units229,3905,779,663
Detached houses44%57%
In buildings of 5 or more15%13%
Mobile homesunder 1%4%
Built before 196058%45%
Built since 20008%14%
Middle year built19571965
Owner-occupied70%69%

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