Miss. Code Ann. § 37-7-725

When a special municipal separate school district embraces and includes all of the territory of the county, then the office of county superintendent of education in such county shall be abolished and discontinued in such county and no county superintendent of education of such county shall be elected at any ensuing elections. In such an event, the superintendent of the special municipal separate school district shall thereafter perform and discharge all duties which would otherwise devolve upon the county superintendent of education under the provisions of any applicable statute of this state, and, for such purpose, the superintendent of such special municipal separate school district shall have and be vested with all power and authority conferred by law upon such county superintendents of education.