On Interstate 94 (Tri-State Tollway) traveling south from Wisconsin, it is the second road seen which has an interchange at that location.

In July 2007, a new interchange was constructed at Illinois 173, Interstates 39/90, and U.S. Route 51 (Jane Addams Memorial Tollway).

SBI Route 173 originally ran from near downtown Rockford (along Forest Hills Road) to Zion.

During the 1980s, when the village of Machesney Park was heavily developed and incorporated, Illinois Route 173 was scaled back and its western terminus moved to Illinois Route 251 (North 2nd Street).

From 1972 to 1994 the highway also assumed a portion of what is now Illinois Route 137 north to the Wisconsin border.