Pennsylvania · county radon data
Radon in Dauphin County, Pennsylvania
55% of the 3,902 home radon tests on record here reached the EPA action level — mid-pack for the state, ranked #21 of 67 tested Pennsylvania counties.
What the numbers say
Dauphin County sits 6 points above the Pennsylvania median (49% of tests over the limit across the state's counties). The median reading among its 3,902 reported tests was 4.8 pCi/L — and the single highest test on record reached 309.7 pCi/L, more than 77× 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 Dauphin County
Underlain by Cambrian–Ordovician limestone and dolomite of Pennsylvania's karst valleys. Karst conduits and clay-rich cavity fill concentrate radium and move radon-laden soil gas quickly — USGS work found roughly a third to two-thirds of tested homes over the EPA action level in these valley counties.
Geology sources: USGS OFR 93-292-C.
The housing stock factor
The median Dauphin County home dates to 1972 — decades before radon-resistant new construction entered building codes. With 289,593 residents largely housed in that older stock, testing is the only way any individual household knows where it stands.
Radon by ZIP in Dauphin 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 |
|---|---|---|---|---|
| 17032 | Halifax | 698 | 73.5% | 416.3 |
| 17023 | Elizabethville | 209 | 62.2% | 90.4 |
| 17061 | Millersburg | 476 | 62% | 119.5 |
| 17109 | Harrisburg | 2,622 | 60% | 509 |
| 17113 | Harrisburg | 609 | 59.3% | 127.3 |
| 17018 | Dauphin | 407 | 59% | 124.3 |
| 17111 | Harrisburg | 4,972 | 55.8% | 10000 |
| 17980 | Tower City | 92 | 53.3% | 100.8 |
| 17036 | Hummelstown | 4,704 | 53.2% | 435.5 |
| 17112 | Harrisburg | 5,316 | 52.7% | 288.7 |
| 17033 | Hershey | 3,063 | 51.7% | 97.7 |
| 17098 | Williamstown | 74 | 48.6% | 89.7 |
| 17104 | Harrisburg | 745 | 45.5% | 111 |
| 17110 | Harrisburg | 3,386 | 39% | 141.2 |
| 17057 | Middletown | 1,560 | 36.8% | 231 |
| 17101 | Harrisburg | 121 | 36.4% | 58 |
| 17034 | Highspire | 146 | 34.2% | 18.2 |
| 17103 | Harrisburg | 455 | 33.2% | 102.8 |
| 17048 | Lykens | 155 | 32.3% | 276.7 |
| 17102 | Harrisburg | 631 | 6.3% | 508 |
Dauphin County in the Pennsylvania picture
| Dauphin County | 55% over the limit | 3,902 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 | 2.3% | |
Ranked nearby in Pennsylvania
- Clinton County — #18, 56.1% of 346 tests over the limit
- Schuylkill County — #19, 55.7% of 2,144 tests over the limit
- Lancaster County — #20, 55.1% of 8,108 tests over the limit
- Warren County — #22, 54.6% of 364 tests over the limit
- Bedford County — #23, 54.4% of 495 tests over the limit
- Carbon County — #24, 54.4% of 818 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).
Dauphin County radon FAQ
- Is radon high in Dauphin County?
- 55% of 3,902 home tests reported to the CDC came back at or above the EPA action level of 4 pCi/L — 6 points above the Pennsylvania county median of 49%, ranking #21 of 67 tested counties. EPA classifies the county as Zone 1.
- Does an older home in Dauphin County mean more radon risk?
- The county's median home was built in 1972 — 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 Dauphin County numbers come from?
- 3,902 aggregated home tests in the CDC's Environmental Public Health Tracking dataset (CDC EPHT 2008-2017). Median reading: 4.8 pCi/L; the highest recorded test hit 309.7 pCi/L. How we handle the data, including its limits, is documented on our methodology page.
- Which ZIP codes in Dauphin County test highest?
- In PA DEP's residential results (1986–2026): 17032 (Halifax) — 73.5% of 698 tests over the limit; 17023 (Elizabethville) — 62.2% of 209 tests over the limit; 17061 (Millersburg) — 62% of 476 tests over the limit. Full ZIP table below.