Radon zone lookup by ZIP code
Type a ZIP code to see which county it sits in and that county’s EPA radon zone. Then test, because the zone is only a county-wide prediction.
Data: EPA Map of Radon Zones (county level, developed 1993; text version downloaded September 2026) and U.S. Census Bureau 2020 ZCTA-to-county relationship file.
Your result appears here
We match your ZIP code to its county or counties, then show each county’s EPA radon zone. If a ZIP crosses county lines, you will see every county and the share of the ZIP’s land in each.
What the three zones mean
In 1993 EPA assigned every U.S. county to one of three radon zones based on indoor radon measurements, geology, aerial radioactivity, soil permeability, and typical foundation types. According to EPA’s fact sheet, Zone 1 counties have a predicted average indoor screening level greater than 4 pCi/L, Zone 2 counties between 2 and 4 pCi/L, and Zone 3 counties less than 2 pCi/L. Roughly a third of counties fall in each zone.
What the zone does not tell you
EPA is direct about this: the Map of Radon Zones “should not be used to determine if individual homes need to be tested.” Radon depends on the soil right under a house and on how the house is built and ventilated. EPA notes that there are many thousands of homes with elevated radon in Zone 2 and Zone 3 counties. The zone is a county-wide average, and your home is not an average. The only way to know your level is to test. See how to test your home.
How we match ZIP codes to counties
ZIP codes are postal routes, not areas, so we use the Census Bureau’s ZIP Code Tabulation Areas (ZCTAs), which approximate them. The 2020 ZCTA-to-county relationship file tells us which counties each ZCTA overlaps and how much land falls in each. When a ZIP crosses county lines, we list every county with at least 1% of its land area, largest first. PO-box-only ZIPs and some business ZIPs have no ZCTA; browse by state instead.
Counties that did not exist in 1993
A few counties have been created or renamed since EPA drew the map (for example, Oglala Lakota County, South Dakota, formerly Shannon County, and several Alaska boroughs). Virginia’s independent cities are not listed separately on EPA’s map. For these we show the zone EPA gave to the predecessor or surrounding county and say so on the result. Puerto Rico and other territories are not covered by the map.
Newer local data
Many states now publish their own radon test results by county or ZIP code, and EPA encourages supplementing the zone map with local data. Each of our state pages links to the state radon program listed by EPA, which is the best place to find newer data, free or discounted test kits, and lists of credentialed professionals.