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Counties with the Highest Radon Potential in Washington

The top 25 of 39 Washington counties on GIS Map, ranked by EPA radon zone, where zone 1 carries the highest predicted indoor radon potential and zone 3 the lowest.

#CountyEPA radon zone
1Chelan County
3
2Clallam County
3
3Cowlitz County
3
4Grays Harbor County
3
5Island County
3
6Jefferson County
3
7King County
3
8Kitsap County
3
9Lewis County
3
10Mason County
3
11Pacific County
3
12Pierce County
3
13San Juan County
3
14Skagit County
3
15Snohomish County
3
16Thurston County
3
17Wahkiakum County
3
18Whatcom County
3
19Adams County
2
20Asotin County
2
21Benton County
2
22Columbia County
2
23Douglas County
2
24Franklin County
2
25Garfield County
2

Source: EPA Map of Radon Zones (September 2025). All counties with data are ranked. Estimates carry margins of error.

Citing this page: GIS Map, “Counties with the Highest Radon Potential in Washington”, https://gismap.land/rankings/washington/highest-radon-counties. Figures from EPA Map of Radon Zones (September 2025).

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