Plaquemines Parish (; Louisiana French: Paroisse des Plaquemines) is a parish located in the U.S. state of Louisiana. As of the 2010 census the population is 23,042. The parish seat is Pointe à la Hache. The parish was formed in 1807.
The name "Plaquemines," in French Creole, was derived from the Atakapa word, piakimin, meaning the local fruit persimmon. The French used it to name a military post they built on the banks of the Mississippi River, as the site was surrounded by numerous persimmon trees. Eventually the name was applied to the entire parish and to a nearby bayou.
The oldest European settlement in the parish was La Balize, where the French built and inhabited a crude fort by 1699 near the mouth of the Mississippi River. The name in French meant "seamark", a tall structure of wood built as a guide for ships. By 1721 the French built one high. A surviving map from about 1720 shows the island and fort, and the mouth of the river.
As traffic and trade on the river increased, so did the importance of river pilots who were knowledgeable about the complicated, ever-changing currents and sandbars in the river. They lived at La Balize with their families. The village was destroyed and rebuilt numerous times, but it was abandoned for good after being destroyed by a September 1860 hurricane. The pilots moved upriver and built the settlement they named Pilottown, which reached its peak of population in the 19th century. The river pilots' expertise continues to be critical, but now they generally live with their families in more populated areas. They stay at Pilottown temporarily for work.
An important historical site is Fort Jackson, built in 1822 as recommended by General Andrew Jackson, hero of the Battle of New Orleans in the War of 1812. In 1861, Fort Jackson served as an important Confederate defense for the city of New Orleans during the Civil War because it was at the mouth of the Mississippi River. The US Army used it as a training base during World War I, 1917-1918.
Plaquemines is one of only two parishes that have kept their same boundaries from the beginning of Louisiana's parishes in 1807 to today, the other being St. Bernard Parish.