The land that became St. Landry Parish was inhabited since at least 10,500 B.C., as deduced from excavations of three prehistoric dwelling sites.

The first European recorded in the Opelousa territory was a French trader named Michel de Birotte.

When the Eastern Attakapas Chief Kinemo sold all the land between Vermilion River and Bayou Teche to Frenchman Gabriel Fuselier de la Claire in 1760, however, the angry Opelousa tribe exterminated the Attakapas (Eastern Atakapa).

Americans from the South and other parts of the United States began to migrate to the area, marking the arrival of the first large English-speaking population and the introduction of the need for more general use of English.

These include Calcasieu, Acadia, Evangeline, Jeff Davis, Beauregard, and Allen.

[4] After Baton Rouge fell to the Union troops during the Civil War in 1862, Opelousas became the state capital for nine months.

A bill was introduced in the Louisiana House of Representatives entitled "An act to create the parish of Nicholls, and to provide for the organization thereof.

Father Joseph Anthonioz, the first pastor of the Catholic Church at Rayne, is credited with having suggested the name, Acadia Parish.

Rumors of Bentley's death, while unfounded, led both Black Republicans and white supremacist Democrats, including the St. Landry Parish chapter of the Knights of the White Camelia, to threaten violent retribution.

In the days following Bentley's subsequent covert flight to New Orleans, the massacre began.

Heavily outnumbered, Black citizens were chased, captured, shot, murdered, and lynched during the following weeks.

While estimates of casualties vary widely, several sources number the deaths between 200 and 300 black people and several dozen whites, making it the bloodiest massacres of the Reconstruction Era and among the deadliest in American history.

Finally, police arrested the vandal who was the son of a St. Landry Parish sheriff's deputy.

[19] As of the 2020 United States census, there were 82,540 people, 30,441 households, and 20,790 families residing in the parish.

It falls under the authority of the Sheriff, who is the chief law enforcement officer of the parish.

[26] The office briefly became the subject of national attention in 2015 when its eccentric Crime Stoppers videos, starring public relations officer (later U.S. Representative) Clay Higgins, went viral and were featured on The Tonight Show Starring Jimmy Fallon.