You'll find them not just at the airports, but sometimes on foot-patrol and/or parade duty downtown (mostly). The most important aspect to know is all CPD officers are required to purchase their own pistol(s). So you are unlikely to see many officers deviate from their original choices.
The following regs:
Officers hired on or before December 1, 1991 may carry DA/SA semi-autos or 4" barreled Colt, Smith and Wesson, or Ruger revolvers in .38 or .357 Magnum.
Officers hired on or before May 19, 2008 may carry DAO S&W, Beretta, Ruger, or Sig Sauer pistols in 9mm, .40, or .45.
Officers hired after August 28, 2015 must choose between Smith and Wesson M&P, Glock 17/19/34, or Springfield Armory XD in 9mm only.
This is per: Chicago Police Department Uniform and Property U04-02
http://directives.chicagopolice.org/...8b.pdf?hl=true
PS: Just noticed while reading through the Uniform and Property code - that sworn officers may not carry more than two
exposed handguns while on duty. I'm not gonna lie, it might be tempting as a CPD officer to rock two handguns.