(a) The membership of any regional planning commission created and established under this article shall be composed of not less than three representatives of each governmental unit participating in the creation of such. In addition to said minimum representation of three, each governmental unit shall be entitled to appoint one other representative for each 50,000 people residing within the geographical and territorial limits and bounds of such governmental unit according to the most recent federal census; provided, that any commission in which any county having a population in excess of 600,000 participates shall be constituted as follows: Each governmental unit shall have only one representative, except that any city having a population of more than 300,000 shall have 20 representatives, and each county having a population of more than 600,000 shall have 10 representatives; provided further, that any commission in which any county having a population between 300,000 and 500,000 according to the most recent federal census participates shall be constituted as follows: Voting representatives from each governmental unit in such number, not less than one for each unit, as shall be agreed upon between all the governmental units forming the region and participating in the regional planning commission on a basis of representation which will give relatively equal representation to each governmental unit according to percentage of its population and its financial contribution to the cost of the commission as related to the total population of the region and the total agreed operating cost of the commission, it being understood that the assessment of operating costs to the member governmental units will be based on the population and area of each such unit as related to the whole population of the region.
(b) Each governmental unit may designate to membership ex officio, and without vote its chief planning officer or chief engineer if it has either, but not both of said officials. The voting members of each such planning commission shall be appointed by the respective governing bodies of the respective governmental units participating. No member of any regional planning commission created under this article shall receive any compensation for his or her services rendered as a member of such regional planning commission, but each such member shall be entitled to receive reimbursement for his or her actual and necessary expenses incurred in the performance of his or her duties as a member of such regional planning commission. Voting members of each regional planning commission created under this article shall be appointed for terms of four years. The terms of ex officio members shall expire with their incumbency in the offices by virtue of which they shall have been designated to membership on such regional planning commission. Vacancies occurring on any such commission shall be filled by the governing body of the governmental unit previously represented by the latest prior occupant of a particular vacant place on such commission.