Napoleonville, the parish seat, is the only incorporated community in the parish. The village is located along the banks of Bayou Lafourche and the first permanent settlements were made in the middle of the eighteenth century by both French and Spanish settlers. The population grew between 1755 and 1764 as exiled Acadians entered the area. Tradition says the area was named by a French settler who had served in the French army under Napoleon Bonaparte. The village has a total area of 0.2 square miles.
Bayou L’Ourse is a community in the southern area of the parish. Bayou L’Ourse has a population of about 1,700. It is home of McDermott Fabricators and the Bayou L’Ourse Nature Trail.
Belle Rose is a census-designated place with a population of 1,944 at the 2000 census. Belle Rose is the home to the Lula Raw Sugar Factory and the Belle Alliance Plantation built in 1847 by Charles Anton Kock. Belle Rose has a total area of 5.4 square miles and is located in the northern part of the parish.
Labadieville, located along Bayou Lafourche, was originally called “Brulee Labadie”. Tradition says that the area was named after French Settler Jean Louis Labadie. Historically, the area was home to the Washi Indian tribe. After 1750, however the population swelled with French, Spanish, Acadian, Islenos, and German settlers. Labadieville is home to St. Philomena Catholic Church, built in 1847, and was also the scene of a battle on October 27, 1862 during the Civil War. Labadieville has a total area of 3.9 square miles.
Pierre Part was founded by Acadian settlers after they were expelled from Canada. Pierre Part was predominantly a fishing community until the Great Depression when many men in town found work in the logging, levee building, and petroleum industries. The Pierre Part and Belle River area encompasses 3.0 square miles and is located in the western part of the parish.
Plattenville is one of the earliest settlements in Assumption. The Church of the Assumption of the Blessed Virgin Mary was built there in 1793, the oldest in the state. Assumption parish was named after this church in 1807. Paincourtville was named, tradition says, after an early traveler was unable to buy a single loaf of bread there and called the area “short of bread town”. Paincourtville is home to St. Elizabeth Catholic Church, built in 1840, which is known for its large church bell which is set in special steel scaffolding outside of the church as it is too large for either of the church’s two towers. Paincourtville has a total area of 1.6 square miles.