Louisiana Highway 142

In the original Louisiana Highway system in use between 1921 and 1955, the modern LA 142 was designated as State Route C-1490.[6] Like all state highways created after 1930, Route C-1490 was numbered by the state highway department rather than by an act of the state legislature and carried a "C-" prefix. The southern terminus was at that time a junction with State Route 204, which followed the modern route of US 425 between Bastrop and the Arkansas state line.[3][6] Apart from the straightening of some curves in the vicinity of Beekman, Route C-1490 remained relatively unchanged until the 1955 Louisiana Highway renumbering.[6][7]

LA 142 was created in 1955 as a direct renumbering of State Route C-1490.[8]

La 142—From the Arkansas state line south of Crossett[,] Arkansas through or near Beekman to a junction with La 139 at or near Chemin A Haut.

— 1955 legislative route description[8]

The southern terminus of the route was now a junction with LA 139. In 1989, US 425 was created and replaced the LA 139 designation north of Bastrop.[9][10]

The route of LA 142 has seen only minor improvements since the 1955 renumbering.[3][11] Most recently, LA 142 was slightly realigned at its southern terminus to intersect US 425 at a right angle. This was done in conjunction with a project completed in April 2012 that widened US 425 to four lanes between Bastrop and the Arkansas state line.[12]