^Southbound trailblazer at Illinois 60 in Vernon Hills, May 2016.
Illinois Route 21 is a north-south route in Chicago's northern suburbs. Since I drove the route from south to north in its entirety, I'm going to list the intersections from south to north on this page. The southern beginning is in Niles, just north of Chicago's north side, and it runs north-northwest as Milwaukee Avenue, to eventually end in Gurnee.
Illinois 21 starts at Illinois 43 in Niles, just outside of the Chicago city limits: