On March 30, 1871, the Louisiana General Assembly passed an act designating the creation of Vernon Parish, by taking territory from the parishes of Natchitoches, Rapides, and Sabine. There are a few stories surrounding the naming of the Parish, none of which have any authentic records as proof. One of them is that it was named in honor of Mt. Vernon, the home of George Washington. The second claims that it was named after a race horse owned by Joe Moore, one of the members of the committee chosen to name the parish, who claimed that by naming the parish after his fast horse the committee would insure the growth of the parish to be as fast as his horse. Originally the area comprising Vernon was apart of a tract of land that was in dispute between the United States and Spain, this land was called the "Neutral Strip." As a result of this dispute the area became a haven for outlaws. Prior to the Louisiana Purchase in 1803, the only persons who came to the area were a few French and Spanish settlers. It was also during this period that Dr. Burr established the community of Burr Ferry. This community was known as the "Gateway to Louisiana". Also located near this community, there still stands an artillery site (now called the "Confederate Breast Works"), which was manned by the Confederacy to guard against Union movements along the "’Nolan Trace" during the Civil War.

Leesville has been the parish seat of Vernon since the parish was created, though it wasn't incorporated until February 15, 1900. The city, although founded by Dr. Edmund E. Smart, was named by Senator R. Smart, his father, in honor of General Robert E. Lee. At the time of Leesville's founding, the site was the home of a plantation owned by Dr. Smart. The house from that plantation may still be found today at the corner of Lula and First street.
 

In 1941, the United States Army opened Camp Polk, shortly after the 1939-40 maneuvers. Camp Polk quickly surpassed the timber industry as the dominant force in the parish's economy, which became evident in the parish seat of Leesville when its population jumped from 3,500 to 18,000 after the camp opened. The Camp receives its name from Leonidas Polk, the first Episcopal Bishop in Louisiana, known as the "Fighting Bishop of the Confederacy" and served as one of the major training camps during World War II. Today, now called Fort Polk is the 5th largest military installation in the nation, containing approximately 200,000 acres (800 km²). With the constant movement of soldiers and their dependents in and out of the parish. Vernon experiences a unique blend of culture from numerous states and countries creating a true "melting pot."