York County, PA is an EPA Radon Zone 1 county, meaning a predicted average indoor screening level above 4 pCi/L. The Pennsylvania Department of Environmental Protection says approximately 40% of homes tested in Pennsylvania read above the EPA action guideline of 4 pCi/L. For scale, the national average indoor level is about 1.3 pCi/L.
PA DEP test results for York County: 98,845 tests, 1986 to 2026. Share of tests at or above 4.0 pCi/L, highest first (tests / 4+ pCi/L / 20+ pCi/L):
Windsor Borough: 864 tests / 67.1% / 28.2%
Dallastown: 2,420 / 65.7% / 23.1%
Fawn Township: 621 / 65.2% / 21.2%
Cross Roads: 952 / 65.2% / 26.3%
Fawn Grove: 460 / 64.8% / 20.4%
East Hopewell Township: 4,344 / 64.6% / 22.9%
Stewartstown: 2,814 / 63.8% / 21.4%
Seven Valleys: 1,543 / 63.4% / 24.7%
North Hopewell Township: 9,107 / 62.2% / 20.9%
Springfield Township: 3,340 / 62% / 22.5%
Chanceford Township: 6,509 / 62% / 21%
Red Lion: 5,341 / 60.9% / 19.7%
Glen Rock: 1,797 / 60.8% / 20.6%
Windsor Township: 16,927 / 57.2% / 16%
York Township: 26,831 / 57% / 16%
Spring Garden Township: 8,348 / 55.2% / 15.2%
Springettsbury Township: 14,747 / 54.1% / 13.5%
York City: 17,149 / 51.9% / 10.3%
West Manchester Township: 12,076 / 50.5% / 7.6%
Conewago Township: 17,245 / 49.1% / 7.7%
Hanover: 11,820 / 47% / 12.4%
Dover Township: 4,041 / 44.2% / 5%
Newberry Township: 3,939 / 41.8% / 6%
York Haven: 1,034 / 40.8% / 4.7%
Wellsville: 440 / 33.6% / 4.5%
ZIP codes cross municipal lines, so neighboring places share some tests. Each figure is the share of tests in that municipality's ZIP codes. The full table of every municipality is on the source page.
Why county averages online disagree
Published York County averages range from roughly 9.85 to 13.2 pCi/L depending on the source. They disagree because they draw on different datasets (often one test-kit vendor's customers), they mix short-term and long-term tests, and people who test are not a random sample of homes. Every published average is biased high to an unknown degree.
What a county or township number cannot tell you
Radon depends on the soil directly beneath one foundation, how permeable it is, the cracks and penetrations in the slab, and how hard the building pulls air up through itself. Two houses on the same street can test several pCi/L apart. A short-term test kit costs about fifteen dollars and answers the question for your house. Basements read higher than upper floors and winter readings run higher than summer ones.
Source and full table: https://radonmitigationyorkpennsylvania.com/york-county-radon-levels
Published by Radon Mitigation York Pennsylvania, 96 S George St, York, PA 17401, (717) 356-9995, https://radonmitigationyorkpennsylvania.com