Wash. Rev. Code § 35.63.070
The commissions of two or more adjoining counties, of two or more adjacent cities and towns, of one or more cities and towns and/or one or more counties, together with the boards of such counties and the councils of such cities and towns may cooperate to form, organize and administer a regional planning commission for the making of a regional plan for the region defined as may be agreed upon by the commissions, boards and councils. The regional commission when requested by the commissions of its region, may further perform any of the other duties for its region that are specified in RCW 35.63.060 for city and county commissions. The number of members of a regional commission, their method of appointment and the proportion of the cost of regional planning, surveys and studies to be borne respectively by the various counties and cities in the region, shall be such as may be agreed upon by commissions, boards and councils.
Any regional planning commission, or the councils or boards respectively of any city, town, or county, are authorized to receive grants-in-aid from the government of the United States or of any of its agencies, and are authorized to enter into any reasonable agreement with any department or agency of the government of the United States to arrange for the receipt of federal funds for planning in the interest of furthering the planning program.
RCW 35.63.070
Commission as employer for retirement system purposes: RCW 41.40.010.