Wash. Rev. Code § 36.08.020
The election shall be conducted in all respects as general elections are conducted under the laws governing general elections, in so far as they may be applicable, except that there shall be triplicate returns made, one to each of the respective county auditors and another to the office of the secretary of state. The ballots used at such election shall contain the words "for transferring territory," or "against transferring territory." The votes shall be canvassed, as by law required, within twenty days, and if three-fifths of the votes cast in the territory at such election are "for transferring territory," the territory described in the petition shall become a part of and be added to and made a part of the county contiguous thereto, and within thirty days after the canvass of the returns of the election, the governor shall issue his or her proclamation of the change of county lines.
RCW 36.08.020