Mandeville is a city in St. Tammany Parish, Louisiana, United States. As of the 2020 United States census, its population was 13,192. Mandeville is located on the north shore of Lake Pontchartrain, south of Interstate 12. It is located directly across the lake from the city of New Orleans and its southshore suburbs. Mandeville is part of the New Orleans-Metairie metropolitan statistical area.