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Radon Levels in Chester County, Pennsylvania

EPA puts Chester County in Zone 1, its highest radon zone, and 24.0% of its 6,770 reported radon tests (2020) 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

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    24.0%

    6.3 pts below PA

    Chester
    24.0%
    PA
    30.3%

    6,770 tests, 2020

  • Median result

    2.0pCi/L

    Below action level

    Chester
    2.0 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2020

  • Tests reported

    6,770

    5th of 63 by tests

    Chester
    6,770
    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

    55 of 63

    Lowest quarter

    Chester
    24.0%
    Perry
    57.7%

    By share, of 63 with 30+ tests

Read a result for Chester County

Starts at Chester County's median, 2.0 pCi/L

2.0pCi/L

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

EPA’s reading of 2.0 pCi/L

Between 2 and 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 between 2 and 4 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Chester County's median reported result, 2020.

Interpret this readingWhat a fix costs

The data

Chester County, At a glance

Chester County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Chester 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 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Chester County, 2020

Share of reported tests at or above 4 pCi/L, by year, Chester County
Share of reported tests at or above 4 pCi/L, by year, Chester County
YearShare of reported tests at or above 4 pCi/L
201427.3%
201527.3%
201626.3%
201727.8%
201826.7%
201927.2%
202024.0%

2020: 24.0%. Across these years the share ran from 24.0% to 27.8%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 6,770 tests reported to CDC for Chester 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

Chester County, Compared

Chester County radon figures, compared

Calculated by Radon411

Chester County's 6,770 reported tests in 2020 had a middle value of 2.0 pCi/L and a maximum of 280.3 pCi/L, and 24.0% reached 4 pCi/L. Pennsylvania as a whole (67 Pennsylvania counties, pooled) comes to 30.3%: 6.3 points higher than here.

Among its state's counties it ranks 55th of 63 Pennsylvania counties with 30 or more tests for the same period. Statewide for the same period, Perry County reported the highest share (57.7%) and Philadelphia County the lowest (10.6%).

Below the action level, 3,333 tests (49.2%) came in under 2 pCi/L, against 44.3% statewide, and 1,811 tests (26.8%) fell between 2 and 4, against 25.4% statewide. The busiest year on file was 2019, with 6,823 tests reported; the quietest, 2014, had 6,158.

EPA's 1993 zone map puts Chester County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 100% of the county's land high radon potential.

Next door, the shares run from 14.7% in Delaware County to 43.3% in Lancaster County, with Montgomery County and Delaware County below Chester County. Over 7 years of annual figures the share fell 3.3 points, from 27.3% in 2014 to 24.0% in 2020; its peak was 27.8% in 2017.

Share of reported tests at or above 4 pCi/L by year, Chester County against Pennsylvania2014 to 2020, years with 30 or more tests: Chester County 27.3% to 24.0%, the state's pooled share 30.3% in 2020.
Chester CountyPennsylvania, pooled
Share of reported tests at or above 4 pCi/L by year, Chester County against Pennsylvania: data table
YearTestsChester County, at or above 4 pCi/LPennsylvania, pooled
20146,15827.3%36.1%
20156,67427.3%37.8%
20166,44726.3%34.4%
20176,52227.8%35.1%
20186,17126.7%30.5%
20196,82327.2%31.4%
20206,77024.0%30.3%
Chester County against Pennsylvania, the United States and nearby counties, 2020
AreaTestsAt or above 4 pCi/LMedianDifference from Chester County
Chester County6,77024.0%2.0 pCi/LThis county
Pennsylvania, pooled67 counties, pooled93,66930.3%Not pooled+6.3 points
United States, pooled915 counties, pooled405,35525.5%Not pooled+1.5 points
Perry Countyhighest in the state18957.7%4.9 pCi/L+33.7 points
Philadelphia Countylowest in the state8,44210.6%1.7 pCi/L−13.4 points
Lancaster County, PAborders it4,39843.3%3.0 pCi/L+19.3 points
Berks County, PAborders it2,63239.6%2.9 pCi/L+15.6 points
Montgomery County, PAborders it10,50821.8%2.0 pCi/L−2.2 points
Delaware County, PAborders it6,04114.7%1.8 pCi/L−9.3 points
Where Chester County's reported results fell, 2020, beside Pennsylvania and the United States
ResultChester County testsChester County sharePennsylvania shareU.S. shareAgainst Pennsylvania
Under 2 pCi/L3,33349.2%44.3%51.6%+4.9 points
2 to 4 pCi/L1,81126.8%25.4%22.9%+1.4 points
4 pCi/L and above1,62624.0%30.3%25.5%−6.3 points
Chester 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
Wayne County50 of 6360730.1%2.3 pCi/L
Crawford County51 of 6322129.9%2.6 pCi/L
Sullivan County52 of 633129.0%2.0 pCi/L
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
Chester County radon tests by year, against Pennsylvania's pooled share
YearTestsAt or above 4 pCi/LMedianHighestPennsylvania, pooledChange from the row before
20206,77024.0%2.0 pCi/L280.3 pCi/L30.3%−3.2 points
20196,82327.2%2.1 pCi/L314.3 pCi/L31.4%+0.5 points
20186,17126.7%2.1 pCi/L1458.0 pCi/L30.5%−1.1 points
20176,52227.8%2.2 pCi/L169.8 pCi/L35.1%+1.5 points
20166,44726.3%2.1 pCi/L241.5 pCi/L34.4%−1.0 points
20156,67427.3%2.2 pCi/L304.0 pCi/L37.8%Level
20146,15827.3%2.2 pCi/L503.5 pCi/L36.1%First on file

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

Chester County, State data

Pennsylvania's own radon test data

Measured

What Pennsylvania's own agencies publish about radon tests in Chester 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 Chester County

Pennsylvania DEP publishes its figures by ZIP code, not by county. These are the 46 ZIP codes that lie wholly or partly in Chester County, each with the state's own figures for it. Period: Period not stated by DEP.

ZIP codes in Chester County
ZIP codeWhat the state reports
17527Basement: average 16.1 pCi/L, 504 tests; First floor: average 7.7 pCi/L, 48 tests
17555Basement: average 9.4 pCi/L, 562 tests; First floor: average 5.2 pCi/L, 47 tests
19073Basement: average 3.0 pCi/L, 4,853 tests; First floor: average 1.8 pCi/L, 871 tests
19087Basement: average 5.7 pCi/L, 12,385 tests; First floor: average 3.6 pCi/L, 2,801 tests
19301Basement: average 6.9 pCi/L, 3,429 tests; First floor: average 5.3 pCi/L, 671 tests
19310Basement: average 10.8 pCi/L, 447 tests; First floor: average 5.1 pCi/L, 57 tests
19311Basement: average 2.9 pCi/L, 1,369 tests; First floor: average 2.7 pCi/L, 103 tests
19312Basement: average 6.2 pCi/L, 5,455 tests; First floor: average 4.0 pCi/L, 1,193 tests
19316Basement: figures not shown; First floor: figures not shown
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
19320Basement: average 10.5 pCi/L, 11,680 tests; First floor: average 6.9 pCi/L, 1,290 tests
19330Basement: average 11.0 pCi/L, 1,008 tests; First floor: average 5.4 pCi/L, 127 tests
19333Basement: average 5.7 pCi/L, 2,459 tests; First floor: average 3.1 pCi/L, 733 tests
19335Basement: average 6.5 pCi/L, 18,589 tests; First floor: average 4.0 pCi/L, 2,374 tests
19341Basement: average 3.3 pCi/L, 5,168 tests; First floor: average 2.0 pCi/L, 825 tests
19342Basement: average 2.7 pCi/L, 3,277 tests; First floor: average 1.6 pCi/L, 509 tests
19343Basement: average 5.1 pCi/L, 3,118 tests; First floor: average 2.8 pCi/L, 373 tests
19344Basement: average 5.6 pCi/L, 1,706 tests; First floor: average 2.8 pCi/L, 188 tests
19345Basement: figures not shown
19348Basement: average 3.8 pCi/L, 5,862 tests; First floor: average 2.3 pCi/L, 806 tests
19350Basement: average 3.2 pCi/L, 2,819 tests; First floor: average 1.9 pCi/L, 342 tests
19352Basement: average 3.9 pCi/L, 1,528 tests; First floor: average 2.1 pCi/L, 171 tests
19355Basement: average 6.5 pCi/L, 9,569 tests; First floor: average 3.8 pCi/L, 1,721 tests
19358Basement: figures not shown; First floor: figures not shown
19362Basement: average 8.0 pCi/L, 592 tests; First floor: average 3.5 pCi/L, 63 tests
19363Basement: average 4.9 pCi/L, 2,485 tests; First floor: average 2.8 pCi/L, 237 tests
19365Basement: average 20.8 pCi/L, 1,703 tests; First floor: average 13.9 pCi/L, 205 tests
19367Basement: average 6.2 pCi/L, 32 tests; First floor: figures not shown
19369Basement: average 32.1 pCi/L, 57 tests; First floor: figures not shown
19372Basement: average 5.2 pCi/L, 623 tests; First floor: average 2.7 pCi/L, 130 tests
19373Basement: average 3.4 pCi/L, 632 tests; First floor: average 1.8 pCi/L, 109 tests
19374Basement: average 3.8 pCi/L, 37 tests; First floor: figures not shown
19375Basement: average 4.8 pCi/L, 143 tests; First floor: average 1.5 pCi/L, 36 tests
19380Basement: average 5.8 pCi/L, 17,528 tests; First floor: average 3.9 pCi/L, 2,906 tests
19382Basement: average 3.0 pCi/L, 13,002 tests; First floor: average 1.8 pCi/L, 2,090 tests
19383Basement: figures not shown; First floor: figures not shown
19390Basement: average 3.2 pCi/L, 2,098 tests; First floor: average 1.8 pCi/L, 261 tests
19425Basement: average 5.1 pCi/L, 6,580 tests; First floor: average 3.7 pCi/L, 729 tests
19442Basement: average 5.2 pCi/L, 230 tests; First floor: average 2.4 pCi/L, 89 tests
19457Basement: figures not shown; First floor: figures not shown
19460Basement: average 4.7 pCi/L, 12,115 tests; First floor: average 2.5 pCi/L, 1,760 tests
19465Basement: average 4.7 pCi/L, 3,634 tests; First floor: average 3.2 pCi/L, 298 tests
19475Basement: average 5.2 pCi/L, 2,377 tests; First floor: average 3.1 pCi/L, 342 tests
19520Basement: average 6.0 pCi/L, 1,375 tests; First floor: average 3.8 pCi/L, 158 tests
19543Basement: average 6.8 pCi/L, 1,298 tests; First floor: average 4.9 pCi/L, 70 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.

Chester County, Geology

The ground under Chester County

Predicted

Most of the ground under Chester County is one class on USGS's geologic map: 99.9% of its land is high radon potential, with 0.1% moderate. The map puts 54.8% of Chester County in the area it calls Piedmont Lowland and 36.2% in Piedmiont Upland, with one smaller area beside them. USGS gives both a radon index of 14, in the high band (12 to 17).

USGS's geologic areas under Chester County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Piedmont LowlandMica schist, phyllite, hornblende gneiss, and marble.High1454.8%
Piedmiont UplandGranitic gneiss, graphitic gneiss, quartz monzonite, quartz monzonite gneiss, granodiorite, and granodiorite gneiss.High1436.2%
Newark BasinGray shale and fluvial sandstone.High128.7%

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

Chester County beside the ground around it

Chester County has more high-potential ground than Pennsylvania as a whole: 99.9% of its land against 70.4%. Of the 6 counties that border it, 3 have more high-potential ground, Berks County the most at 100%.

Share of land by USGS radon potential: Chester County, the 6 counties bordering it and Pennsylvania
AreaEPA zoneLow potentialModerate potentialHigh potential
Chester CountyZone 1None0.1%99.9%
Delaware CountyZone 1None23.4%76.6%
Montgomery CountyZone 1NoneNone100%
Lancaster CountyZone 1NoneNone100%
New Castle County, DEZone 235.7%63.8%None
Berks CountyZone 1NoneNone100%
Cecil County, MDZone 220.0%35.4%38.0%
Pennsylvania67 counties, pooled by land areaVaries0.7%28.9%70.4%

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

Local help

Chester County, Local resources

Radon testing and mitigation in Chester County

Listed radon businesses with an address in Chester County:

Listed radon professionals by town: Phoenixville, West Chester, Coatesville, Atglen

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

Chester County, Questions

Questions about radon in Chester County

Are radon levels high in Chester County?

In 2020, 24.0% of the radon tests reported to CDC for Chester County, Pennsylvania were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.0 pCi/L. Of 63 Pennsylvania counties with 30 or more tests for the same period, 54 reported a higher share; pooled, the state comes to 30.3%.

Which counties border Chester County?

Chester County borders 6 counties: Delaware County, PA, Montgomery County, PA, Lancaster County, PA, New Castle County, DE, Berks County, PA and Cecil County, MD.

Products

Chester County, Products

Testing a home in Chester County

In Chester County, 24.0% of 6,770 tests reported to CDC in 2020 reached 4 pCi/L, against 30.3% pooled across Pennsylvania. In Zone 1 the year-round level in Chester 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

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

Explore

Chester County, Bordering counties

Counties bordering Chester County

Calculated by Radon411

Chester County, Cities and towns

Cities and towns in Chester County

The Census Bureau estimates 557,116 residents in Chester County for July 1, 2025, 22,258 more than in 2020 (+4.2%). That works out to 742 people per square mile of land. No town dominates: Phoenixville, the largest, has 20,356 residents, 3.7% of the total. Together its 16 incorporated places hold 17.4% of those residents; the other 82.6% live outside any of them. Testing is reported here more often than across the state: CDC's 6,770 reported tests for 2020 come to 12.2 for every 1,000 residents (2025 estimate), against 7.2 for Pennsylvania.

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

The 12 largest cities and towns in Chester County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Phoenixville20,356+9.5%3.7%
West Chester19,591+4.9%3.5%
Coatesville13,283−0.4%2.4%
Downingtown8,384+4.8%1.5%
Kennett Square6,893+16.0%1.2%
Oxford5,887+2.7%1.1%
Parkesburg3,976+2.3%0.7%
Spring City3,878+11.4%0.7%
Malvern3,427+0.4%0.6%
West Grove2,835+2.2%0.5%
Honey Brook1,891+0.1%0.3%
South Coatesville1,773+10.2%0.3%
  • Atglen
  • Elverson
  • Avondale
  • Modena

16 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).

Chester County, Homes

Homes in Chester County

Of Chester County's 210,730 homes, 60% are detached houses, against 57% across Pennsylvania; 14% are in buildings of five or more homes. Much of Chester County is recent building: 25% of its homes have gone up since 2000 and the middle year built is 1983, against 1965 for Pennsylvania. 75% 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 Chester County, Pennsylvania, 2019 to 2023
HomesChester CountyPennsylvania
Housing units210,7305,779,663
Detached houses60%57%
In buildings of 5 or more14%13%
Mobile homes2%4%
Built before 196023%45%
Built since 200025%14%
Middle year built19831965
Owner-occupied75%69%

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