Illinois Route 128 is a north-south highway along the west edge of what I'd call "east-central Illinois". It runs through a corridor that starts southeast of Decatur, and runs south to a point along Interstate 70 west of Effingham.
Illinois 128's northern end is at Illinois 121 southeast of Mount Zion:
At Shelbyville, Illinois 128 joins Illinois 16 westward for a few miles:
Then, Illinois 128 departs from Illinois 16 to continue south:
Illinois 128 meets the western end of Illinois 33 near Beecher City:
Having almost reached its end, Illinois 128 joins US Route 40 east for three miles: