Mary Gillen Montgomery High School is located in Semmes, an incorporated suburb of Mobile in Mobile County, Alabama, United States. Founded in 1965, the school is part of the Mobile County Public School System, and is one of the largest of the county's 18 public high schools. Due to its long official name, the school is affectionately known as "MGM," "Mary G," "Mary Montgomery," or "Montgomery High." The school serves: Semmes and the community of Wilmer, the latter formerly an incorporated municipality.