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Radon by state and county
State radon data, licensing rules and radon mitigation costs for the states and counties we cover. Each page cites the state program or EPA file its numbers come from.
Pennsylvania statewide guide37.3% of 2.64 million Pennsylvania basement radon tests read 4 pCi/L or higher (PA DEP). ZIP results, DEP-certified mitigators and typical system costs.
→Ohio statewide guide34.4% of 525,229 Ohio radon tests read 4 pCi/L or higher (Ohio Dept. of Health). County results, ODH-licensed mitigators and typical system costs.
→York County, Pennsylvania56.3% of 85,880 basement radon tests in York County ZIPs read 4 pCi/L or higher (PA DEP data). Local results, DEP certification rules and system costs.
→Centre County, PennsylvaniaCentre County basement radon tests: 56.3% of 40,153 read 4 pCi/L or higher (PA DEP data). State College ZIP results, DEP rules and mitigation costs.
→Chester County, PennsylvaniaChester County logged 234,595 basement radon tests in PA DEP data; 31.1% read 4 pCi/L or higher. ZIP results from West Chester to Coatesville, and costs.
→Lebanon County, Pennsylvania60.0% of 27,006 basement radon tests in Lebanon County ZIPs hit 4 pCi/L or more (PA DEP data). Local ZIP results, DEP certification and system costs.
→Adams County, Pennsylvania43.2% of 14,835 basement radon tests in Adams County ZIPs read 4 pCi/L or more (PA DEP data). Gettysburg-area results, DEP rules and mitigation costs.
→Snyder County, PennsylvaniaSnyder County basement radon tests: 50.8% of 5,187 read 4 pCi/L or higher (PA DEP data). Selinsgrove and Middleburg results, DEP rules and system costs.
→Washington County, PennsylvaniaWashington County, PA: 34.3% of 39,398 basement radon tests read 4 pCi/L or higher (PA DEP data), though EPA rates it Zone 2. ZIP results and system costs.
→Delaware County, Ohio49.64% of 23,086 radon tests in Delaware County, Ohio read 4 pCi/L or higher (Ohio Dept. of Health). Licensing rules, local geology and system costs.
→Maricopa County, ArizonaEPA rates Maricopa County Zone 2, a predicted average of 2 to 4 pCi/L. What that means for Phoenix-area slab homes, who installs systems, and typical costs.
→Eagle County, ColoradoEagle County is EPA Zone 2, while 53 of Colorado's 64 counties are Zone 1 (EPA map). Licensing since 2022, mountain-home factors and mitigation costs.
→New Haven County, ConnecticutNew Haven County is EPA Zone 1, one of 4 Connecticut counties rated highest (EPA map). State contractor rules for radon work, well water and system costs.
→Barnstable County, MassachusettsBarnstable County is EPA Zone 2 (2 to 4 pCi/L predicted). Cape Cod sandy soils, private wells, Massachusetts contractor rules and radon mitigation costs.
→Norfolk County, MassachusettsNorfolk County is EPA Zone 2, yet one of its 40 ZIP areas spans all 3 EPA zones (Census and EPA files). Granite bedrock, contractor rules and system costs.
→Clay County, MinnesotaClay County is EPA Zone 1, like 68 of Minnesota's 87 counties (EPA map). MDH licensing, Red River Valley clay soils and radon mitigation costs in Moorhead.
→Buncombe County, North CarolinaBuncombe County is one of only 8 North Carolina counties EPA rates Zone 1. Blue Ridge geology, state guidance, free test kits and radon mitigation costs.
→Prince William County, VirginiaPrince William County is EPA Zone 2, while 45 of Virginia's 95 counties are Zone 1 (EPA map). Virginia's certification law, local geology and system costs.
→Laramie County, WyomingLaramie County is EPA Zone 1, as are 21 of Wyoming's 23 counties (EPA map). Free state test kits, granite geology and radon mitigation costs in Cheyenne.
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