Washington County Codes

In 1935, Washington began to issue license plates by county. A one- or two-letter prefix denoted the county, and letters were assigned by the order of population, with King County, the most populous, receiving letter A, followed by Pierce with B, and so on. After letter Z, the 13 smallest counties received two-letter prefixes derived from the county name.

1935 County Plates cropped
This photo from the Washington State Archives shows a complete county set from the first year of county coding, taken on the steps of the northeast corner of the state capitol
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This c.1935 advertising card from the New Richmond laundry of Seattle showed a handy map of the new county codes

For the first six years, the passenger vehicle class was the only license plate type to receive a county code.  Starting in 1941, truck and trailer formats were adapted to include county codes. In 1954 the system remained the same, except the county code became a suffix. 

With the adoption of a modern ABC 123 numbering format for passenger vehicles in 1958, the county codes were modified to a three-letter format as shown below (county coding was discontinued for truck and trailer plates).  By 1980 the system became too complex to manage and the state discontinued the practice.

CountySeat1935-19571958-1981
KingSeattleAAAA-AZZ, OAA-OZZ, IAA-IZZ, UCA-UKZ
PierceTacomaBBAA-BZZ, TBA-TFZ
SpokaneSpokaneCCAA-CZZ, SLA-SMZ (excl CLx, CMx, CUx)
SnohomishEverettDDAA-DVR (excl DSA-DUZ)
YakimaYakimaEEAA-EKZ
WhatcomBellinghamFFAA-FFP
ClarkVancouverGGAA-GND, HHA-HHZ
Grays HarborMontesanoHHAA-HDP
KitsapPort OrchardIKSA-KYZ
ThurstonOlympiaJJAA-JEE
ChelanWenatcheeKKAA-KDC
LewisChehalisLLAA-LDG
SkagitMount VernonMMAA-MDS
CowlitzKelsoNNAA-NFR
Walla WallaWalla WallaOWWA-WYP
WhitmanColfaxPPAA-PCF
ClallamPort AngelesQCLA-CMZ, PDA-PDF
BentonProsserRRAA-REU
KittitasEllensburgSSAA-SBH
LincolnDavenportTTAA-TAN
OkanoganOkanoganUUAA-UBJ
PacificSouth BendVVAA-VAW
StevensColvilleWWAA-WBC
MasonSheltonXXAA-XAZ
JeffersonPort TownsendYYAA-YAM
KlickitatGoldendaleZZAA-ZBD
AdamsRitzvilleADYYA-YYR
AsotinAsotinANZYA-ZYL, ZZA-ZZZ
ColumbiaDaytonCOCUA-CUG
DouglasWatervilleDODSA-DST
FranklinPascoFNFNA-FSF
FerryRepublicFYFYA-FYE
GarfieldPomeroyGAGDA-GDF
GrantEphrataGTGTA-GVW
IslandCoupevilleIS1958: CVA-CVL   1963 up: ISA-ITH
Pend OreilleNewportPOPEB-PES
San JuanFriday HarborSJSJA-SJG
SkamaniaStevensonSASKA-SKJ
WahkiakumCathlametWAWMA-WMF
Dept. of LicensingJJJJA-JJZ, XXA-XXZ
Dept. of Licensing (1939-1942)LD