Wash. Rev. Code § 36.145.080
(2) Except as provided in subsection (3) of this section, if the proposed district is located entirely within a single jurisdiction, then the board of supervisors consists of:
(3) If all or a portion of the proposed district is located within unincorporated land that is entirely surrounded by an incorporated city or town, then the board of supervisors consists of:
(4) If the county, city, or town is the exclusive legislative authority pursuant to RCW 36.145.010, then the board of supervisors consists of:
[ 2010 c 7 s 301.]