St. Tammany Parish is a parish located in the U.S. state of Louisiana named after Tamanend, the legendary Lenape Chief of Chiefs and the "Patron Saint of America." At the 2020 census, the population was 264,570, making it the fourth-most populous parish in Louisiana. The parish seat is Covington. The parish was founded in 1810. St. Tammany Parish comprises the Slidell–Mandeville–Covington metropolitan statistical area, which is also included in the New Orleans–Metairie–Slidell combined statistical area.