The route provides the most direct connection between Bastrop, the parish seat, and northbound US 165, which heads north from Bonita toward the Arkansas state line.

US 165 takes a more indirect routing, heading eastward out of Bastrop before turning north at Mer Rouge.

From the west, LA 140 begins at an intersection with US 425 in a rural area known as Log Cabin, 3.1 miles (5.0 km) northeast of Bastrop.

It proceeds northeast along Old Bonita Road, and the area gradually becomes sparsely populated over the next several miles.

[2][3][4] Soon after resuming its northeastern course, the surroundings abruptly change from thick forest to open farmland.

[6][2] LA 140 is an undivided two-lane highway for its entire length with a posted speed limit of 55 mph (90 km/h).

[11] US 425 was established in 1989 following the existing route of LA 139 from the Arkansas state line south to Bastrop.