A portion of the Great River Road was on an old railroad alignment, which you can see parts of just north of Alton.

North of Hardin, the highway follows the west bank of the Illinois River until the bridge near Florence.

From that point on, IL 100 follows mostly farmland on much higher ground until Beardstown, where it will cross the river a third and final time.

In 1987, IL 3, 143, and 100 alignments were changed to their current routes in the River Bend (Illinois) area when the Homer M. Adams Parkway Extension was opened.

Inspections suggested that continued use of the lift span could harm the structural integrity of the bridge.