Garyville is a census-designated place in St. John the Baptist Parish, Louisiana, United States. The population was 2,775 at the 2000 census and 2,123 in 2020. It is part of the New Orleans–Metairie–Kenner Metropolitan Statistical Area. The Garyville Refinery, built in 1976 by Marathon Petroleum Company, is the third-largest oil refinery in the United States.