Washington Revised Code Title 42. Public Officers and Agencies § 42.12.040. Vacancy in partisan elective office--Successor elected--When

(1) If a vacancy occurs in any partisan elective office in the executive or legislative branches of state government or in any partisan county elective office before the first day of the regular filing period, the position must be open for filing during the regular filing period as provided in RCW 29A.24.171 and a successor shall be elected at the general election. Except during the last year of the term of office, if such a vacancy occurs on or after the first day of the regular filing period, the election of the successor shall occur at the next succeeding general election as provided in RCW 29A.24.171. The elected successor shall hold office for the remainder of the unexpired term. This section shall not apply to any vacancy occurring in a charter county which has charter provisions inconsistent with this section.

(2) If a vacancy occurs in any legislative office or in any partisan county office after the general election in a year that the position appears on the ballot and before the start of the next term, the term of the successor who is of the same party as the incumbent may commence once he or she has qualified as defined in RCW 29A.04.133 and shall continue through the term for which he or she was elected.