Wash. Rev. Code § 36.64.080
The boards of county commissioners of any county and any counties contiguous thereto and the governing body of any cities and/or towns within said counties may establish and organize a regional agency hereinafter referred to as a conference, for the purpose of studying regional and governmental problems of mutual interest and concern, including but not limited to, facility studies on highways, transit, airports, ports or harbor development, water supply and distribution, codes and ordinances, governmental finances, flood control, air and water pollution, recommendations of sites for schools and educational institutions, hospitals and health facilities, parks and recreation, public buildings, land use and drainage; and to formulate recommendations for review and action by the member counties and/or cities legislative body.
RCW 36.64.080
Youth agencies, joint establishment: RCW 35.21.630.