Chicago, Illinois is a rarely used location in comics. It has seen the likes of Supergirl, Hawkman, Deadpool, Blue Beetle, The Avengers, The Green Hornet and others. The Wizard Harry Dresden calls it home.
When the character of Blue Beetle was bought by DC Comics from Charlton Comics Chicago was used as his base of operations and home. This is most likely do to it's similarity to Hub City a fictional city used by Blue Beetle and the Question in Charlton Comics, though Hub City still exists in the DCU. In the DC Universe Blue Beetle (Ted Kord) had huge ties to the city. It is where his international company of K.O.R.D. Incorporated was headquartered as well as having a prominent S.T.A.R. Labs location that was taken over by the founder of S.T.A.R. Labs, Garrison Slate.