Radon Testing & Mitigation in Chester County, PA
31% of 211,728 basement radon tests reported to PA DEP in Chester County measured 4.0 pCi/L or higher, EPA's action level (median 2.4 pCi/L).
Connect with a DEP-Certified Radon Professional
or call(717) 461-2427
Radon in Chester County: 31% of the 211,728 basement tests reported to PA DEP measured 4.0 pCi/L or higher, EPA's action level, 6 points below the 37% statewide share. The county ranks 58th highest of 67, and the median result is 2.4 pCi/L. Only a test shows one home's level.
Radon Test Results by ZIP Code in Chester County
52 ZIP codes in Chester County have at least 20 basement tests on record. Among those with 100 or more, the highest share at or above 4.0 pCi/L is in 19310 (Atglen): 60% of 646 tests. The lowest is in 19317 (Chadds Ford): 13% of 513 tests.
| ZIP code | Post office | Basement tests | Median pCi/L | At or above 4.0 |
|---|---|---|---|---|
| 19335 | Downingtown | 27,775 | 2.6 | 35% |
| 19380 | West Chester | 25,601 | 2.1 | 29% |
| 19382 | West Chester | 19,936 | 1.8 | 18% |
| 19320 | Coatesville | 17,233 | 3.5 | 46% |
| 19460 | Phoenixville | 16,343 | 2.2 | 27% |
| 19355 | Malvern | 15,175 | 2.6 | 36% |
| 19425 | Chester Springs | 10,217 | 2.4 | 31% |
| 19348 | Kennett Square | 9,242 | 2.3 | 26% |
| 19312 | Berwyn | 8,137 | 2.5 | 35% |
| 19341 | Exton | 7,269 | 2.0 | 21% |
| 19301 | Paoli | 4,867 | 2.9 | 42% |
| 19465 | Pottstown | 4,804 | 2.6 | 32% |
| 19350 | Landenberg | 4,433 | 2.0 | 21% |
| 19343 | Glenmoore | 4,337 | 2.8 | 36% |
| 19087 | Wayne | 4,138 | 2.2 | 28% |
Show all 52 ZIP codes
| 19333 | Devon | 3,754 | 2.4 | 33% |
| 19363 | Oxford | 3,650 | 2.9 | 37% |
| 19475 | Spring City | 3,603 | 2.6 | 32% |
| 19390 | West Grove | 3,507 | 2.2 | 23% |
| 19311 | Avondale | 2,451 | 1.9 | 19% |
| 19352 | Lincoln University | 2,418 | 2.2 | 25% |
| 19365 | Parkesburg | 2,331 | 4.6 | 55% |
| 19344 | Honey Brook | 2,245 | 2.7 | 36% |
| 19520 | Elverson | 1,736 | 3.3 | 42% |
| 19330 | Cochranville | 1,549 | 4.1 | 51% |
| 19372 | Thorndale | 846 | 2.6 | 36% |
| 19362 | Nottingham | 743 | 3.8 | 49% |
| 19310 | Atglen | 646 | 5.3 | 60% |
| 19317 | Chadds Ford | 513 | 1.6 | 13% |
| 19481 | Valley Forge | 275 | 2.6 | 29% |
| 19442 | Kimberton | 262 | 3.6 | 43% |
| 19375 | Unionville | 148 | 2.6 | 34% |
| 19421 | Birchrunville | 119 | 2.8 | 31% |
| 19342 | Glen Mills (part) | 107 | 1.8 | 22% |
| 19395 | Westtown | 102 | 1.8 | 16% |
| 19073 | Newtown Square (part) | 95 | 1.5 | 7% |
| 19360 | New London | 94 | 2.4 | 29% |
| 19543 | Morgantown (part) | 79 | 1.8 | 23% |
| 19374 | Toughkenamon | 66 | 2.9 | 30% |
| 19369 | Sadsburyville | 62 | 15.2 | 92% |
| 19347 | Kemblesville | 57 | 2.4 | 23% |
| 19480 | Uwchland | 53 | 2.9 | 45% |
| 19383 | West Chester | 48 | 2.0 | 25% |
| 19358 | Modena | 43 | 3.5 | 47% |
| 19367 | Pomeroy | 37 | 4.6 | 65% |
| 19318 | Chatham | 35 | 3.2 | 40% |
| 19357 | Mendenhall | 33 | 2.1 | 21% |
| 19470 | Saint Peters | 27 | 3.2 | 30% |
| 19354 | Lyndell | 23 | 4.9 | 65% |
| 19376 | Wagontown | 23 | 6.0 | 61% |
| 19316 | Brandamore | 21 | 1.9 | 24% |
| 19366 | Pocopson | 20 | 4.9 | 65% |
| Chester County | 211,728 | 2.4 | 31% | |
| Pennsylvania | 2,629,492 | 2.8 | 37% | |
See your ZIP in the table?
Get matched with a DEP-certified radon professionalFirst-floor tests in Chester County: 27,547 on record, median 1.5 pCi/L, 20% at or above 4.0 pCi/L.
EPA's Map of Radon Zones (1993) places Chester County in Zone 1, its highest category (predicted average indoor screening level above 4 pCi/L). The map is a county-wide prediction; the figures in this table are measurements.
Figures count tests, not homes. A home tested more than once is counted each time, and tests run after a mitigation system was installed are included because the dataset does not separate them. ZIP codes with fewer than 20 basement tests are not shown.
Housing Age in Chester County
45% of Chester County's 212,491 housing units were built before 1980, 22 points below the 67% statewide figure; 13% date from before 1940. Those homes predate EPA's 1994 model standards for radon-resistant construction. Age does not predict a test result: EPA's guidance is that any home, new or old, may have a radon problem.
Source: U.S. Census Bureau, American Community Survey 2020–2024 5-year estimates, table B25034. Counts all housing units, including vacant and seasonal ones. Retrieved September 29, 2026.
Bedrock Under Chester County
Glenarm Wissahickon formation (probably lower Paleozoic; mica schist) underlies 24% of the county. Felsic and intermediate gneiss (Precambrian; gneiss) underlies 14% of the county. Graphitic felsic gneiss (Precambrian; gneiss) underlies 10% of the county.
Some gneiss, schist and phyllite carry naturally elevated uranium, and the USGS has identified faults and shear zones in these rocks as sites of localized uranium concentration.
Mapped bedrock describes an area. The USGS states that its radon assessment cannot be applied to individual homes. More on Pennsylvania radon and geology.
Sources: U.S. Geological Survey State Geologic Map Compilation, from Pennsylvania Geological Survey Map 1 (1980; digital edition 2001). Retrieved September 29, 2026. U.S. Geological Survey Open-File Report 93-292-C, Geologic Radon Potential of EPA Region 3 (1993).
Private Wells in Chester County
An estimated 41% of Chester County residents supplied their own household water in 2015, typically from a private well. Radon dissolves in groundwater and is released into indoor air when water is used for showering and other household purposes. EPA's guidance: if an air test finds a radon problem and your water comes from a well, have the water tested too. A water test is separate from an air test.
Sources: U.S. Geological Survey, Estimated Use of Water in the United States, county-level data for 2015. Retrieved September 29, 2026. U.S. EPA, A Citizen's Guide to Radon.
Home Purchases in Chester County
Lenders reported 5,275 home-purchase mortgages originated in Chester County in 2024. The count covers financed purchases only; cash purchases are not in the data. See radon in a Pennsylvania home sale.
Selling or buying? See radon mitigation for a home sale in Chester County for disclosure timing, who pays, and how a post-mitigation retest fits before settlement.
Source: FFIEC Home Mortgage Disclosure Act data, 2024. Retrieved September 29, 2026.
Municipalities in Chester County
Chester County has 73 municipalities: 1 city, 15 boroughs and 57 townships.
Show all 73 municipalities
Atglen borough, Avondale borough, Birmingham township, Caln township, Charlestown township, Coatesville city, Downingtown borough, East Bradford township, East Brandywine township, East Caln township, East Coventry township, East Fallowfield township, East Goshen township, East Marlborough township, East Nantmeal township, East Nottingham township, East Pikeland township, East Vincent township, East Whiteland township, Easttown township, Elk township, Elverson borough, Franklin township, Highland township, Honey Brook borough, Honey Brook township, Kennett township, Kennett Square borough, London Britain township, London Grove township, Londonderry township, Lower Oxford township, Malvern borough, Modena borough, New Garden township, New London township, Newlin township, North Coventry township, Oxford borough, Parkesburg borough, Penn township, Pennsbury township, Phoenixville borough, Pocopson township, Sadsbury township, Schuylkill township, South Coatesville borough, South Coventry township, Spring City borough, Thornbury township, Tredyffrin township, Upper Oxford township, Upper Uwchlan township, Uwchlan township, Valley township, Wallace township, Warwick township, West Bradford township, West Brandywine township, West Caln township, West Chester borough, West Fallowfield township, West Goshen township, West Grove borough, West Marlborough township, West Nantmeal township, West Nottingham township, West Pikeland township, West Sadsbury township, West Vincent township, West Whiteland township, Westtown township, Willistown township.
Source: U.S. Census Bureau, 2025 Gazetteer Files, county subdivisions. Retrieved September 29, 2026.
City Pages in Chester County
Neighboring Counties
- Radon in Berks County → 51% of 77,953 basement tests at or above 4.0 pCi/L
- Radon in Delaware County → 20% of 151,091 basement tests at or above 4.0 pCi/L
- Radon in Lancaster County → 55% of 109,065 basement tests at or above 4.0 pCi/L
- Radon in Montgomery County → 28% of 295,317 basement tests at or above 4.0 pCi/L
- All 67 Pennsylvania county radon pages
DEP-Certified Mitigation Firms Based in County
3 DEP-certified mitigation firms are physically based in Chester County. Firms from adjacent counties routinely serve here as well.
Source: PA DEP Certified Mitigation Firms Directory, July 2026. This reflects business address only — firms based elsewhere may also serve Chester County.
Testing, Cost and Certification
Short-term tests run 48–96 hours; long-term tests run 90 days or more. At 4.0 pCi/L or higher, retest or mitigate. How radon testing works in a Pennsylvania real estate transaction.
Mitigation in Chester County typically costs $1,050–$2,700. Pennsylvania radon mitigation cost guide.
Anyone testing or mitigating for pay must hold DEP certification under 25 Pa. Code § 240. How to verify a contractor in the PA DEP Radon Services Directory.
Frequently Asked Questions
What share of radon tests in Chester County are at or above the EPA action level?
31% of the 211,728 basement tests reported to PA DEP from Chester County measured 4.0 pCi/L or higher, against 37% statewide. The median result is 2.4 pCi/L, and 5% of tests measured 20 pCi/L or higher.
Which Chester County ZIP code has the highest radon test results?
Among ZIP codes with at least 100 basement tests, 19310 (Atglen) has the highest share at or above 4.0 pCi/L: 60% of 646 tests, with a median of 5.3 pCi/L. 19317 (Chadds Ford) has the lowest, at 13%.
How does Chester County compare with other Pennsylvania counties?
Chester County ranks 58th highest of 67 counties by share of basement tests at or above 4.0 pCi/L, at 31%. Among its neighbors, Lancaster County has the highest share at 55% and Delaware County the lowest at 20%.
What bedrock is under Chester County?
The largest mapped units are Glenarm Wissahickon formation (24% of the county), Felsic and intermediate gneiss (14% of the county) and Graphitic felsic gneiss (10% of the county), according to the USGS compilation of the Pennsylvania Geological Survey state map.
Should Chester County well owners test their water for radon?
An estimated 41% of Chester County residents supplied their own household water in 2015. EPA's guidance is to test the air first. If the air test finds a radon problem and the water comes from a well, have the water tested as well.