Port Sulphur is a census-designated place (CDP) on the West Bank of the Mississippi River in Plaquemines Parish, Louisiana, United States. The population was 1,760 at the 2010 census.
The name Port Sulphur derives from the Freeport Sulphur Company in the early 1930s, when it set up logistics, refining, storage and shipping operations to support its Frasch Process sulphur mine at Lake Grande Ecaille, located 10 miles west of the town in the nearby marsh. The Grande Ecaille mine was the largest sulphur deposit in the world when it began operation in 1933, and remained in production until 1978. Over time, as other discoveries were made, the Freeport Sulphur Company also used the Port Sulphur facility to support their other Frasch Process sulphur mines located at Garden Island Bay, Lake Pelto, and Caillou Island; a land-based mine at Chacahoula; the first offshore sulphur mines at Grand Isle and Caminada Pass; and a large operation 50 miles offshore from the Mississippi River Delta in 300 feet of water, at Main Pass Block 299 in the Gulf of Mexico. The facility was also used to process and ship recovered sulphur obtained by oil and gas refining. The terminal was able to filter and store liquid hot molten sulphur in large insulated heated tanks, and "vat" liquid sulphur into acres of long term dry storage by forming blocks of bright yellow sulphur by spraying molten sulphur into metal forms on the ground and allowing to cool. The site is valuable because of its proximity to sulphur producing areas near the Gulf of Mexico, its docking sites along the Mississippi River and back bay marsh.