The first two digits are the county code, and if there were any cities listed, they are the third digit, otherwise the third digit is 0.
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010 Adams County
020 Asotin County
030 Benton County
031 Kennewick
032 Richland
033 Prosser
040 Chelan County
042 Wenatchee
050 Clallam County
052 Port Angeles
060 Clark County
062 Vancouver
063 Camas
070 Columbia County
073 Dayton
080 Cowlitz County
082 Longview
083 Kelso
090 Douglas County
100 Ferry County
110 Franklin County
112 Pasco
120 Garfield County
130 Grant County
133 Grand Coulee
134 Ephrata
135 Moses Lake
140 Grays Harbor County
141 Aberdeen
142 Hoquiam
150 Island County
160 Jefferson County
163 Port Townsend
170 King County
171 Seattle
172 Renton
173 Auburn
174 Enumclaw
175 Kent
176 Kirkland
180 Kitsap County
182 Bremerton
190 Kittitas County
193 Ellensburg
200 Klickitat County
210 Lewis County
213 Centralia
214 Chehalis
220 Lincoln County
230 Mason County
233 Shelton
240 Okanogan County
243 Omak
250 Pacific County
253 Raymond
260 Pend Oreille County
270 Pierce County
271 Tacoma
272 Puyallup
273 Sumner (in original listing here: 237, perhaps a mistake)
274 Buckley
280 San Juan County
290 Skagit County
293 Anacortes
294 Mount Vernon
295 Sedro Woolley
300 Skamania County
310 Snohomish County
312 Everett
313 Snohomish
320 Spokane County
321 Spokane City
323 Medical Lake
324 Cheney
330 Stevens County
333 Colville
340 Thurston County
342 Olympia
343 Tumwater
350 Wahkiakum County
360 Walla Walla County
362 Walla Walla City
363 College Place
370 Whatcom County
372 Bellingham
380 Whitman County
382 Pullman
383 Colfax
390 Yakima County
392 Yakima City
393 Sunnyside
394 Toppenish
395 Grandview
396 Wapato
-- Thanks to
N.P. Maling
Seattle, King, Washington
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