RCW 27.12.010 (8): "… a municipal corporation organized to provide library service for a portion of the unincorporated area of a county. Any city or town located in the same county as a rural partial-county library district may annex to the district if the city or town has a population of one hundred thousand or less at the time of annexation."
May be created in a portion of the unincorporated area of a county if a rural county library district, intercounty rural library district, or island library district has not already been created in the county.
See also RCW 27.12.470.
May annex any city or town with a population of 100,000 or less at the time of annexation (RCW 27.12.010(8)) and adjacent unincorporated territory in the county.
See also RCW 27.12.470.
By vote of registered voters within the governmental unit in which the library is located as prescribed in RCW 27.12.030.
See also RCW 27.12.320.