Miss. Code Ann. § 17-1-29

Any two or more counties and municipalities are hereby authorized and empowered to create and to establish a regional planning commission to be composed of representatives appointed thereto by each county board of supervisors and municipal legislative body desiring representation on such commission, and to appropriate monies from their respective public funds for the purposes of carrying out the provisions of Sections 17-1-31 through 17-1-35 , inclusive. The regional planning commission shall be composed of not to exceed three representatives from each participating county and not to exceed two representatives from each participating municipality; provided, however, the regional planning commission membership shall not exceed fifteen in number. Participating governmental units may designate to membership ex officio and without vote the chairman of the local planning commission and/or the city or county engineer. Counties or municipalities within the State of Mississippi may join with adjacent counties, parishes, and/or municipalities in adjoining states to form an interstate regional planning commission.