Mo. Rev. Stat. § 230.110

If, and when, the state highways and transportation commission is authorized by law so to do, and may so desire it may take over all or any part of the highways of the county highway system and make refund therefor in such manner as may now or hereafter be provided by law for making refund to the several counties of this state, and road districts thereof, for highways heretofore designated and taken over by said state transportation department, whereupon it shall be the duty of the county highway commission, by proper deed of conveyance, to transfer to state transportation department that part of county highway system so taken over.