Illinois Route 173 (IL 173) is a 66.20-mile-long (106.54 km) east–west state road that runs from Illinois Route 251 in the Rockford suburb of Machesney Park east to Illinois Route 137 (Sheridan Road/Buckley) in Zion near the Illinois-Wisconsin border. Illinois Route 173 is also one of the northernmost east-west state highways in Illinois. On Interstate 94 (Tri-State Tollway) traveling south from Wisconsin, it is the second road seen which has an interchange at that location. Similarly, when traveling south/east from Wisconsin on Interstate 39/90 (Jane Addams Memorial Tollway), Illinois Route 173 is only the third exit into Illinois. In 2008, the entirety of Illinois 173 has been designated the 173rd Airborne Brigade Highway