Washington: 39 counties covered
Of 39 rated Washington counties, 7 are in EPA's highest radon-potential zone (Zone 1) — but every county page links to testing guidance regardless of zone, because a county rating is a county-wide average, not a reading for any one house.
- King County
- Pierce County
- Snohomish County
- Spokane County
- Clark County
- Thurston County
- Kitsap County
- Yakima County
- Whatcom County
- Benton County
- Skagit County
- Cowlitz County
- Grant County
- Franklin County
- Lewis County
- Island County
- Chelan County
- Clallam County
- Grays Harbor County
- Mason County
- Walla Walla County
- Stevens County
- Whitman County
- Kittitas County
- Douglas County
- Okanogan County
- Jefferson County
- Pacific County
- Klickitat County
- Asotin County
- Adams County
- San Juan County
- Pend Oreille County
- Skamania County
- Lincoln County
- Ferry County
- Wahkiakum County
- Columbia County
- Garfield County