It runs from Illinois Route 37 at Pulleys Mill (near the intersection of Interstate 24 and Interstate 57) north to the western terminus of Illinois Route 142 and Illinois 37 south of downtown Mount Vernon.

[1] Illinois 148 is a western parallel of Illinois 37 from Pulleys Mill to Mount Vernon.

It is a two-laned surface road for its entire length.

SBI Route 148 ran from Marion to Mount Vernon.

In 1964 it was extended south to Pulleys Mill.