A 1993 map, a 2026 map of counties

EPA's Map of Radon Zones has not changed its underlying assessment since 1993, but US county boundaries have — Connecticut abolished its 8 counties for 9 Census "Planning Regions" in 2022, and Alaska has split or renamed several boroughs and census areas since 1993 (Valdez-Cordova into Chugach and Copper River Census Areas, for one). Where a current county doesn't correspond 1:1 to the county EPA originally scored, this site reports no zone rather than guessing.

What it looks like in practice

16 of the 3,144 counties and county-equivalents in this dataset fall into this gap: 9 Connecticut Planning Regions and 7 Alaska boroughs/census areas. Every other county — including two tricky historical cases this site did resolve, Oglala Lakota County, SD (renamed from Shannon County in 2015) and Doña Ana County, NM (an accent-mark mismatch between EPA's plain-text spelling and the Census Bureau's) — gets a real EPA zone.

Why not guess

Connecticut's old counties don't map cleanly onto the new Planning Regions — several old counties are split across more than one region — and Alaska's newer census areas were carved out of larger 1993-era ones in ways that aren't a simple rename either. Assigning either group a zone borrowed from a neighbor would be a guess dressed up as data, so this site says plainly where EPA's map doesn't reach instead.

Where to go next

See the range this plays out across: Loving County, TX, Logan County, KY, Middlesex County, MA.

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