@Canageek this is the wrong state, but for minnesota it was 1937 http://www.dli.mn.gov/CCLD/ElectricalHistory.asp (or maybe you already found that :/ ). i can't seem to find an equivalent history page on washington state's licensing site though :(
@bunnyhero @allan found the answer for Washington! Thanks
@Canageek oh i was skimming too fast. as early as 1899 it was required for counties of 125000+ people