It runs from Illinois Route 3 near Grimsby east to Illinois Route 34 in Thompsonville.

This is a distance of 45.92 miles (73.90 km).

[1] Illinois 149 runs east–west through downtown Murphysboro and to the north of Carbondale.

Through West Frankfort, Illinois 149 doubles as "Main Street."

SBI Route 149 originally ran from Hurst to Thompsonville.