Miss. Code § 65-11-17
The board of supervisors of the several counties and the State Highway Commission are hereby authorized and directed to enter into such contracts and cooperative agreements with each other and with any appropriate federal agency that may be necessary to carry out the purposes of Sections 65-11-1 through 65-11-37 and that may be necessary to enable the state and counties to participate in and avail themselves of any funds apportioned to the state under the Federal Aid Highway Act of 1944 [58 U. S. Stat. 838, ch. 626]. The boards of supervisors and the State Highway Commission are further authorized and directed to do any and all other things that may be necessary to carry out the purposes of said sections, within their respective jurisdictions. It is hereby expressly declared that nothing contained in the cited sections shall be deemed to convert any highway into a state highway or to place same on the state highway system unless and until such highway is placed on the state system in the manner prescribed by law; nor shall any action or step taken under the provisions of such sections (including the improvement or construction of any county highway) convert any highway into a state highway.
Miss. Code § 65-11-17