Pennsylvania · county radon data
Radon in Chester County, Pennsylvania
29.3% of the 11,038 home radon tests on record here reached the EPA action level — toward the lower end of the state's tested counties, ranked #62 of 67 tested Pennsylvania counties.
What the numbers say
Chester County sits 19.7 points below the Pennsylvania median (49% of tests over the limit across the state's counties). The median reading among its 11,038 reported tests was 2.2 pCi/L — and the single highest test on record reached 315.8 pCi/L, more than 78× the action level. EPA maps place the county in Radon Zone 1 — its highest-potential category, where average indoor screening levels are predicted above 4 pCi/L.
Why: the ground under Chester County
Sits on or beside the Reading Prong — a belt of uranium-bearing Precambrian granite and gneiss that produces some of the highest indoor radon readings in the United States. This is the geology behind the famous 1984 Stanley Watras case in Berks County (a home near Boyertown measured extreme radon), the discovery that launched America's radon programs. Fractured crystalline rock and thin soils let radon move efficiently into basements.
Geology sources: USGS OFR 93-292-C · PA DEP Radon Division · Watras/Boyertown 1984 (PMC4629742).
The housing stock factor
The median Chester County home dates to 1983 — decades before radon-resistant new construction entered building codes. With 547,840 residents largely housed in that older stock, testing is the only way any individual household knows where it stands.
Radon by ZIP in Chester County
Pennsylvania is one of the few states publishing actual test results at ZIP level (PA DEP residential data, 1986–2026) — county averages hide a lot; this doesn't.
| ZIP | Place | Tests | % ≥ 4 pCi/L | Max |
|---|---|---|---|---|
| 19369 | Sadsburyville | 58 | 93.1% | 258 |
| 19367 | Pomeroy | 33 | 60.6% | 11.4 |
| 19310 | Atglen | 473 | 58.6% | 169.3 |
| 19330 | Cochranville | 1,217 | 49.3% | 282.8 |
| 19365 | Parkesburg | 1,762 | 48.8% | 1530 |
| 19362 | Nottingham | 576 | 45.1% | 95.2 |
| 19358 | Modena | 36 | 44.4% | 52.7 |
| 19320 | Coatesville | 14,263 | 44.3% | 1122.8 |
| 19383 | West Chester | 33 | 42.4% | 9.5 |
| 19301 | Paoli | 4,220 | 40.6% | 135.6 |
| 19520 | Elverson | 227 | 37.9% | 66.4 |
| 19363 | Oxford | 3,071 | 36.2% | 181.6 |
| 19343 | Glenmoore | 3,387 | 35.2% | 124.5 |
| 19335 | Downingtown | 23,569 | 34.3% | 408.1 |
| 19465 | Pottstown | 494 | 34% | 117.2 |
| 19372 | Thorndale | 738 | 33.9% | 155 |
| 19312 | Berwyn | 7,044 | 33.8% | 176.9 |
| 19374 | Toughkenamon | 63 | 33.3% | 10.3 |
| 19355 | Malvern | 13,388 | 32.9% | 304 |
| 19460 | Phoenixville | 2,253 | 31.8% | 183 |
| 19475 | Spring City | 3,043 | 31.1% | 164.6 |
| 19333 | Devon | 3,696 | 29.4% | 196.6 |
| 19425 | Chester Springs | 8,165 | 29.1% | 162.2 |
| 19442 | Kimberton | 36 | 27.8% | 33.5 |
| 19087 | Wayne | 3,625 | 27% | 1458 |
| 19375 | Unionville | 143 | 26.6% | 54.9 |
| 19380 | West Chester | 23,183 | 25.6% | 801 |
| 19352 | Lincoln University | 2,065 | 23.8% | 201.4 |
| 19348 | Kennett Square | 8,819 | 23.7% | 322.75 |
| 19390 | West Grove | 3,125 | 22.3% | 114.5 |
| 19350 | Landenberg | 3,863 | 19.3% | 103.1 |
| 19311 | Avondale | 2,087 | 19.1% | 43.9 |
| 19341 | Exton | 6,789 | 19% | 137 |
| 19317 | Chadds Ford | 445 | 13.3% | 18.7 |
| 19382 | West Chester | 76 | 9.2% | 6.9 |
Chester County in the Pennsylvania picture
| Chester County | 29.3% over the limit | 11,038 tests |
| Pennsylvania's highest: Fulton County | 69.7% | 90 tests |
| Pennsylvania county median | 49% | 67 counties ranked |
| Share of all Pennsylvania tests from this county | 6.4% | |
Ranked nearby in Pennsylvania
- Crawford County — #59, 33.4% of 878 tests over the limit
- Wayne County — #60, 32.5% of 209 tests over the limit
- Erie County — #61, 31.8% of 6,605 tests over the limit
- Bucks County — #63, 27.5% of 9,078 tests over the limit
- Montgomery County — #64, 27.2% of 14,749 tests over the limit
- McKean County — #65, 26.4% of 144 tests over the limit
(Ranking neighbors — counties adjacent in the Pennsylvania test ranking, not necessarily on the map.)
High test? Fixes and real pricing: the Pennsylvania mitigation cost guide. Every statistic here traces to the methodology (CDC EPHT (labs), 2008–2017; zones: EPA; year built & population: ACS 5-year; ZIP results: PA DEP).
Chester County radon FAQ
- Is radon high in Chester County?
- 29.3% of 11,038 home tests reported to the CDC came back at or above the EPA action level of 4 pCi/L — 19.7 points below the Pennsylvania county median of 49%, ranking #62 of 67 tested counties. EPA classifies the county as Zone 1.
- Does an older home in Chester County mean more radon risk?
- The county's median home was built in 1983 — before radon-resistant construction practices entered building codes in the 1990s, so most of the housing stock has no built-in radon protection. Construction age changes the odds, not the answer: only a test tells you about your house.
- Where do these Chester County numbers come from?
- 11,038 aggregated home tests in the CDC's Environmental Public Health Tracking dataset (CDC EPHT 2008-2017). Median reading: 2.2 pCi/L; the highest recorded test hit 315.8 pCi/L. How we handle the data, including its limits, is documented on our methodology page.
- Which ZIP codes in Chester County test highest?
- In PA DEP's residential results (1986–2026): 19369 (Sadsburyville) — 93.1% of 58 tests over the limit; 19367 (Pomeroy) — 60.6% of 33 tests over the limit; 19310 (Atglen) — 58.6% of 473 tests over the limit. Full ZIP table below.