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Radon Levels in Montgomery County, Pennsylvania

EPA puts Montgomery County in Zone 1, its highest radon zone, and 21.8% of its 10,508 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

    21.8%

    8.5 pts below PA

    Montgomery
    21.8%
    PA
    30.3%

    10,508 tests, 2020

  • Median result

    2.0pCi/L

    Below action level

    Montgomery
    2.0 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2020

  • Tests reported

    10,508

    Most tested in PA

    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

    58 of 63

    Lowest quarter

    Montgomery
    21.8%
    Perry
    57.7%

    By share, of 63 with 30+ tests

Read a result for Montgomery County

Starts at Montgomery 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. Montgomery County's median reported result, 2020.

Interpret this readingWhat a fix costs

The data

Montgomery County, At a glance

Montgomery County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Montgomery 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 Montgomery County, 2020

Share of reported tests at or above 4 pCi/L, by year, Montgomery County
Share of reported tests at or above 4 pCi/L, by year, Montgomery County
YearShare of reported tests at or above 4 pCi/L
201426.2%
201526.5%
201624.8%
201725.7%
201823.0%
201922.1%
202021.8%

2020: 21.8%. Across these years the share ran from 21.8% to 26.5%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 10,508 tests reported to CDC for Montgomery 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

Montgomery County, Compared

Montgomery County radon figures, compared

Calculated by Radon411

Montgomery County's 10,508 reported tests in 2020 had a middle value of 2.0 pCi/L and a maximum of 204.9 pCi/L, and 21.8% reached 4 pCi/L. Pennsylvania as a whole (67 Pennsylvania counties, pooled) comes to 30.3%: 8.5 points higher than here.

Among its state's counties it ranks 58th 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, 5,113 tests (48.7%) came in under 2 pCi/L, against 44.3% statewide, and 3,103 tests (29.5%) fell between 2 and 4, against 25.4% statewide. The busiest year on file was 2019, with 10,751 tests reported; the quietest, 2014, had 8,934.

EPA's 1993 zone map puts Montgomery 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 10.6% in Philadelphia County to 39.8% in Lehigh County, with Delaware County and Philadelphia County below Montgomery County. Over 7 years of annual figures the share fell 4.4 points, from 26.2% in 2014 to 21.8% in 2020; its peak was 26.5% in 2015.

Share of reported tests at or above 4 pCi/L by year, Montgomery County against Pennsylvania2014 to 2020, years with 30 or more tests: Montgomery County 26.2% to 21.8%, the state's pooled share 30.3% in 2020.
Montgomery CountyPennsylvania, pooled
Share of reported tests at or above 4 pCi/L by year, Montgomery County against Pennsylvania: data table
YearTestsMontgomery County, at or above 4 pCi/LPennsylvania, pooled
20148,93426.2%36.1%
20159,80726.5%37.8%
201610,22624.8%34.4%
201710,29425.7%35.1%
201810,38223.0%30.5%
201910,75122.1%31.4%
202010,50821.8%30.3%
Montgomery County against Pennsylvania, the United States and nearby counties, 2020
AreaTestsAt or above 4 pCi/LMedianDifference from Montgomery County
Montgomery County10,50821.8%2.0 pCi/LThis county
Pennsylvania, pooled67 counties, pooled93,66930.3%Not pooled+8.5 points
United States, pooled915 counties, pooled405,35525.5%Not pooled+3.7 points
Perry Countyhighest in the state18957.7%4.9 pCi/L+35.9 points
Fayette Countylowest in the state28717.4%1.8 pCi/L−4.4 points
Lehigh County, PAborders it3,10339.8%2.7 pCi/L+18.0 points
Berks County, PAborders it2,63239.6%2.9 pCi/L+17.8 points
Chester County, PAborders it6,77024.0%2.0 pCi/L+2.2 points
Bucks County, PAborders it7,06623.2%2.0 pCi/L+1.4 points
Delaware County, PAborders it6,04114.7%1.8 pCi/L−7.1 points
Philadelphia County, PAborders it8,44210.6%1.7 pCi/L−11.2 points
Where Montgomery County's reported results fell, 2020, beside Pennsylvania and the United States
ResultMontgomery County testsMontgomery County sharePennsylvania shareU.S. shareAgainst Pennsylvania
Under 2 pCi/L5,11348.7%44.3%51.6%+4.4 points
2 to 4 pCi/L3,10329.5%25.4%22.9%+4.1 points
4 pCi/L and above2,29221.8%30.3%25.5%−8.5 points
Montgomery 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
Montgomery County radon tests by year, against Pennsylvania's pooled share
YearTestsAt or above 4 pCi/LMedianHighestPennsylvania, pooledChange from the row before
202010,50821.8%2.0 pCi/L204.9 pCi/L30.3%−0.3 points
201910,75122.1%2.1 pCi/L78.8 pCi/L31.4%−0.9 points
201810,38223.0%2.1 pCi/L281.7 pCi/L30.5%−2.7 points
201710,29425.7%2.3 pCi/L769.7 pCi/L35.1%+0.9 points
201610,22624.8%2.2 pCi/L180.6 pCi/L34.4%−1.7 points
20159,80726.5%2.3 pCi/L303.0 pCi/L37.8%+0.3 points
20148,93426.2%2.3 pCi/L145.3 pCi/L36.1%First on file

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

Montgomery County, State data

Pennsylvania's own radon test data

Measured

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

Pennsylvania DEP publishes its figures by ZIP code, not by county. These are the 71 ZIP codes that lie wholly or partly in Montgomery County, each with the state's own figures for it. Period: Period not stated by DEP.

ZIP codes in Montgomery County
ZIP codeWhat the state reports
18041Basement: average 4.8 pCi/L, 647 tests; First floor: average 2.7 pCi/L, 126 tests
18054Basement: average 4.7 pCi/L, 635 tests; First floor: average 2.7 pCi/L, 111 tests
18070Basement: average 8.8 pCi/L, 114 tests; First floor: figures not shown
18073Basement: average 4.5 pCi/L, 1,575 tests; First floor: average 2.2 pCi/L, 202 tests
18074Basement: average 3.7 pCi/L, 982 tests; First floor: average 2.0 pCi/L, 156 tests
18076Basement: average 3.4 pCi/L, 357 tests; First floor: average 1.8 pCi/L, 55 tests
18914Basement: average 5.3 pCi/L, 6,254 tests; First floor: average 2.9 pCi/L, 1,201 tests
18915Basement: average 3.1 pCi/L, 251 tests; First floor: average 2.1 pCi/L, 35 tests
18936Basement: average 3.3 pCi/L, 318 tests; First floor: average 1.7 pCi/L, 101 tests
18964Basement: average 3.7 pCi/L, 2,395 tests; First floor: average 1.8 pCi/L, 453 tests
18969Basement: average 3.8 pCi/L, 2,572 tests; First floor: average 2.1 pCi/L, 543 tests
19001Basement: average 3.3 pCi/L, 3,855 tests; First floor: average 2.1 pCi/L, 1,231 tests
19002Basement: average 4.3 pCi/L, 9,243 tests; First floor: average 2.6 pCi/L, 1,954 tests
19003Basement: average 2.5 pCi/L, 3,078 tests; First floor: average 1.3 pCi/L, 723 tests
19004Basement: average 4.0 pCi/L, 3,050 tests; First floor: average 2.0 pCi/L, 596 tests
19006Basement: average 4.4 pCi/L, 5,146 tests; First floor: average 2.5 pCi/L, 1,211 tests
19009Basement: average 7.2 pCi/L, 129 tests; First floor: average 3.7 pCi/L, 41 tests
19010Basement: average 3.2 pCi/L, 4,858 tests; First floor: average 1.7 pCi/L, 1,151 tests
19012Basement: average 3.3 pCi/L, 1,794 tests; First floor: average 2.4 pCi/L, 442 tests
19025Basement: average 3.7 pCi/L, 1,780 tests; First floor: average 1.9 pCi/L, 409 tests
19027Basement: average 4.5 pCi/L, 3,409 tests; First floor: average 2.2 pCi/L, 794 tests
19031Basement: average 4.7 pCi/L, 1,395 tests; First floor: average 2.5 pCi/L, 321 tests
19034Basement: average 3.9 pCi/L, 1,897 tests; First floor: average 2.5 pCi/L, 465 tests
19035Basement: average 4.5 pCi/L, 1,593 tests; First floor: average 3.2 pCi/L, 329 tests
19038Basement: average 4.1 pCi/L, 6,178 tests; First floor: average 2.4 pCi/L, 1,422 tests
19040Basement: average 3.4 pCi/L, 3,463 tests; First floor: average 1.9 pCi/L, 808 tests
19041Basement: average 3.9 pCi/L, 1,595 tests; First floor: average 1.9 pCi/L, 348 tests
19044Basement: average 4.3 pCi/L, 3,019 tests; First floor: average 2.2 pCi/L, 1,057 tests
19046Basement: average 5.4 pCi/L, 4,404 tests; First floor: average 3.4 pCi/L, 938 tests
19066Basement: average 3.9 pCi/L, 1,983 tests; First floor: average 1.8 pCi/L, 401 tests
19072Basement: average 4.4 pCi/L, 3,187 tests; First floor: average 2.5 pCi/L, 685 tests
19075Basement: average 4.0 pCi/L, 2,212 tests; First floor: average 2.4 pCi/L, 566 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
19087Basement: average 5.7 pCi/L, 12,385 tests; First floor: average 3.6 pCi/L, 2,801 tests
19090Basement: average 2.4 pCi/L, 3,062 tests; First floor: average 1.5 pCi/L, 934 tests
19095Basement: average 5.6 pCi/L, 1,423 tests; First floor: average 3.3 pCi/L, 340 tests
19096Basement: average 3.1 pCi/L, 4,474 tests; First floor: average 1.9 pCi/L, 960 tests
19118Basement: average 4.5 pCi/L, 2,852 tests; First floor: average 2.4 pCi/L, 854 tests
19128Basement: average 3.2 pCi/L, 6,261 tests; First floor: average 2.1 pCi/L, 1,180 tests
19401Basement: average 2.9 pCi/L, 4,852 tests; First floor: average 1.8 pCi/L, 1,262 tests
19403Basement: average 4.5 pCi/L, 10,231 tests; First floor: average 2.5 pCi/L, 2,092 tests
19405Basement: average 3.0 pCi/L, 722 tests; First floor: average 1.9 pCi/L, 112 tests
19406Basement: average 4.4 pCi/L, 4,378 tests; First floor: average 3.8 pCi/L, 946 tests
19422Basement: average 3.9 pCi/L, 6,232 tests; First floor: average 2.1 pCi/L, 1,610 tests
19426Basement: average 4.2 pCi/L, 12,309 tests; First floor: average 2.5 pCi/L, 1,783 tests
19428Basement: average 3.5 pCi/L, 3,917 tests; First floor: average 2.3 pCi/L, 800 tests
19435Basement: average 4.9 pCi/L, 36 tests; First floor: figures not shown
19436Basement: average 5.4 pCi/L, 82 tests; First floor: figures not shown
19437Basement: average 5.3 pCi/L, 448 tests; First floor: average 2.3 pCi/L, 102 tests
19438Basement: average 3.8 pCi/L, 5,671 tests; First floor: average 2.3 pCi/L, 1,107 tests
19440Basement: average 3.4 pCi/L, 3,158 tests; First floor: average 1.6 pCi/L, 802 tests
19444Basement: average 3.8 pCi/L, 3,057 tests; First floor: average 2.6 pCi/L, 833 tests
19446Basement: average 4.1 pCi/L, 13,140 tests; First floor: average 2.0 pCi/L, 3,243 tests
19453Basement: average 9.4 pCi/L, 165 tests; First floor: figures not shown
19454Basement: average 3.7 pCi/L, 6,636 tests; First floor: average 1.9 pCi/L, 1,767 tests
19456Basement: average 4.8 pCi/L, 166 tests; First floor: average 2.6 pCi/L, 41 tests
19460Basement: average 4.7 pCi/L, 12,115 tests; First floor: average 2.5 pCi/L, 1,760 tests
19462Basement: average 4.0 pCi/L, 2,156 tests; First floor: average 2.4 pCi/L, 589 tests
19464Basement: average 4.0 pCi/L, 8,254 tests; First floor: average 2.2 pCi/L, 1,063 tests
19468Basement: average 4.3 pCi/L, 6,399 tests; First floor: average 2.7 pCi/L, 859 tests
19472Basement: figures not shown; First floor: figures not shown
19473Basement: average 3.6 pCi/L, 3,542 tests; First floor: average 2.2 pCi/L, 530 tests
19474Basement: average 3.0 pCi/L, 522 tests; First floor: average 1.3 pCi/L, 148 tests
19477Basement: average 4.3 pCi/L, 132 tests; First floor: average 1.5 pCi/L, 44 tests
19490Basement: average 5.4 pCi/L, 340 tests; First floor: average 2.7 pCi/L, 93 tests
19492Basement: average 7.8 pCi/L, 127 tests; First floor: figures not shown
19504Basement: average 10.7 pCi/L, 1,036 tests; First floor: average 7.9 pCi/L, 133 tests
19505Basement: average 8.2 pCi/L, 497 tests; First floor: average 4.5 pCi/L, 40 tests
19512Basement: average 10.6 pCi/L, 2,668 tests; First floor: average 6.6 pCi/L, 238 tests
19525Basement: average 4.1 pCi/L, 3,305 tests; First floor: average 2.4 pCi/L, 247 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.

Montgomery County, Geology

The ground under Montgomery County

Predicted

USGS's geologic map puts all of Montgomery County's mapped land in one class: high radon potential. The map puts 81.3% of Montgomery County in the area it calls Newark Basin and 18.4% in Piedmont Lowland. USGS gives the first a radon index of 12 and the second 14, both in the high band (12 to 17).

USGS's geologic areas under Montgomery County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Newark BasinGray shale and fluvial sandstone.High1281.3%
Piedmont LowlandMica schist, phyllite, hornblende gneiss, and marble.High1418.4%

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

Montgomery County beside the ground around it

Montgomery County has more high-potential ground than Pennsylvania as a whole: 100% of its land against 70.4%. Of the 6 counties that border it, none has as large a share of high-potential ground; Berks County comes nearest at 100%.

Share of land by USGS radon potential: Montgomery County, the 6 counties bordering it and Pennsylvania
AreaEPA zoneLow potentialModerate potentialHigh potential
Montgomery CountyZone 1NoneNone100%
Bucks CountyZone 1None11.0%89.0%
Philadelphia CountyZone 3None63.6%36.5%
Delaware CountyZone 1None23.4%76.6%
Chester CountyZone 1None0.1%99.9%
Lehigh CountyZone 1NoneNone100%
Berks CountyZone 1NoneNone100%
Pennsylvania67 counties, pooled by land areaVaries0.7%28.9%70.4%

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

Local help

Montgomery County, Local resources

Radon testing and mitigation in Montgomery County

Listed radon businesses with an address in Montgomery County:

Listed radon professionals by town: Pottstown, Lansdale, Collegeville, Royersford, Green Lane

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

Montgomery County, Questions

Questions about radon in Montgomery County

Are radon levels high in Montgomery County?

In 2020, 21.8% of the radon tests reported to CDC for Montgomery 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, 57 reported a higher share; pooled, the state comes to 30.3%.

Which counties border Montgomery County?

Montgomery County borders 6 counties: Bucks County, Philadelphia County, Delaware County, Chester County, Lehigh County and Berks County.

Products

Montgomery County, Products

Testing a home in Montgomery County

In Montgomery County, 21.8% of 10,508 tests reported to CDC in 2020 reached 4 pCi/L, against 30.3% pooled across Pennsylvania. In Zone 1 the year-round level in Montgomery 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

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

Explore

Montgomery County, Bordering counties

Counties bordering Montgomery County

Calculated by Radon411

Montgomery County, Cities and towns

Cities and towns in Montgomery County

The Census Bureau estimates 877,643 residents in Montgomery County for July 1, 2025, 20,814 more than in 2020 (+2.4%). Packed into its land, that is 1,817 people per square mile. No town dominates: Norristown, the largest, has 35,911 residents, 4.1% of the total. Testing is reported here more often than across the state: CDC's 10,508 reported tests for 2020 come to 12.0 for every 1,000 residents (2025 estimate), against 7.2 for Pennsylvania.

From Norristown to Green Lane, CDC publishes no figure by town: each reads Montgomery County's.

The 12 largest cities and towns in Montgomery County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Norristown35,911+0.5%4.1%
Pottstown23,322−0.4%2.7%
Lansdale18,986+0.8%2.2%
Conshohocken9,266+0.2%1.1%
Hatboro8,593+2.5%1.0%
Souderton7,288+2.8%0.8%
Ambler6,840+0.4%0.8%
Bridgeport5,758+14.8%0.7%
Collegeville5,287+4.8%0.6%
Telfordextends beyond Montgomery County4,978+1.1%Counted whole
Royersford4,888−0.2%0.6%
Jenkintown4,785+1.7%0.5%
  • Narberth
  • Trappe
  • Pennsburg
  • Hatfield
  • North Wales
  • East Greenville
  • Rockledge
  • Red Hill
  • West Conshohocken
  • Bryn Athyn
  • Schwenksville
  • Green Lane

24 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. “(part)” marks a place that extends into another county. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond Montgomery County is counted whole, so it has no share.

Montgomery County, Homes

Homes in Montgomery County

Fewer than six in ten of Montgomery County's 348,696 homes are detached houses (54%, against 57% across Pennsylvania); the rest are attached, in shared buildings or mobile. Half of its homes were built before 1970, close to Pennsylvania's 1965: 38% date from before 1960 and 16% from 2000 or later. 72% 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 Montgomery County, Pennsylvania, 2019 to 2023
HomesMontgomery CountyPennsylvania
Housing units348,6965,779,663
Detached houses54%57%
In buildings of 5 or more19%13%
Mobile homes1%4%
Built before 196038%45%
Built since 200016%14%
Middle year built19701965
Owner-occupied72%69%

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