Radon zones by state

Pick a state to see every county’s EPA radon zone and a link to the state radon program. The bar next to each state shows its share of Zone 1 (red), Zone 2 (orange), and Zone 3 (yellow) counties.

How to read the state pages

Each state page lists every county with the zone EPA assigned on its 1993 Map of Radon Zones. Zone 1 counties have a predicted average indoor screening level above 4 pCi/L, Zone 2 between 2 and 4 pCi/L, and Zone 3 below 2 pCi/L. The prediction is based on indoor measurements, geology, aerial radioactivity, soil permeability, and foundation types, averaged across a whole county.

That is useful for spotting regions where radon is common, but it cannot tell you about your house. EPA’s advice is to test every home no matter which zone it is in, and to fix homes at or above 4 pCi/L. Your state radon program, linked on each page, often has newer local testing data and can point you to free or discounted test kits and credentialed professionals.

Where the county list comes from

County names follow the 2020 Census. EPA’s map dates from 1993, so a few counties created or renamed since then, along with Virginia’s independent cities, are shown with the zone EPA gave the predecessor or surrounding county, and are labeled that way. Puerto Rico and the other territories are not covered by the zone map. When your state program publishes newer test results by county or ZIP code, trust those over the 1993 zone.

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