(1) The county governing authority of any county may appoint a developmental disability board to plan services for persons with developmental disabilities, to provide directly or indirectly a continuum of care and services to persons with developmental disabilities within the county or counties served by the community board. The governing authorities of more than one county by joint action may appoint a single developmental disability board. Nothing in this section shall prohibit a county or counties from combining the developmental disability board with another county board, such as a mental health board.

(2) Members appointed to the board shall include but not be limited to representatives of public, private, or voluntary agencies, representatives of local governmental units, and citizens knowledgeable about developmental disabilities or interested in services to persons with developmental disabilities in the community.

(3) The board shall consist of not less than nine nor more than fifteen members.

(4) Members shall be appointed for terms of three years and until their successors are appointed and qualified.

(5) The members of the developmental disability board shall not be compensated for the performance of their duties as members of the board, but may be paid subsistence rates and mileage in the amounts prescribed by RCW 42.24.090.