Mandeville is a city in St. Tammany Parish, Louisiana, United States. Its population was 11,560 at the 2010 U.S. census, and 13,192 at the 2020 United States census. Mandeville is located on the north shore of Lake Pontchartrain, south of Interstate 12. It is across the lake from the city of New Orleans and its southshore suburbs. It is part of the New Orleans–Metairie–Kenner metropolitan area.