SR 142 begins in McNairy County in Selmer at an intersection with US 45/SR 5 south of downtown.

The highway then turns southeast to pass through West Shiloh, where it has an intersection with SR 117, before crossing into Hardin County.

They go south along the western edge of Shiloh National Military Park to arrive at Shiloh, where SR 142 splits off and goes south through wooded and hilly areas to pass by Childers Hill to enter Southside and come to an intersection with SR 57.

It goes west along SR 57 for a short distance before turning south again through wooded areas to come to an end at the Mississippi state line, where it continues as Alcorn County Road 100 to Mississippi Highway 350 (MS 350), which is less than half a mile away, and the town of Farmington.

[2] The entire route of SR 142 is a two-lane highway.