Yeah, Chicago is pretty nice. I'm guessing it's pretty popular because of the breadth of programs there. You have Northwestern and UofChicago, Rush for the big time names. UIC and Loyola for very solid programs with good reputations, Cook County and Illinois-Masonic for good clinical stuff without much name. So that's 7 programs that attract all 3 levels of applicants, from people going for the big name programs, to people just hoping to match somewhere.
There are also a lot of med schools in the midwest and a lot of people want to train in a big city. Well there is no big city outside of Chicago in the midwest and Detroit doesn't count.
Oh, I forgot to say what makes Chicago great as a city...
Well they have a good public transportation system. Lots of great bars and clubs. Good shopping. It's really nice in the summertime with the lake right there. Very diverse population. Lots of good restaurants. Housing is expensive, but not NYC expensive. $1100 should get a nice one-bedroom downtown from the apartment books that I picked up when I was there. A couple of hours to the north there is some nice vacationing areas in Wisconsin, Lake Geneva and so on. Some great pro sports teams: Cubs, White Sox, Blackhawks and Da Bears! And finally...the BEST food in my opinion. Pizza, Chicago style. Hot dogs, Chicago style. And the annual Taste of Chicago.
there are multiple 4 O'clock (in tha morn) bars open every day of the week if that gives you any indication to the amount of liquor consumed in this city. Weekends most clubs open till 5, most bars open till 4, some clubs open till 6am. Best food around. Shopping up the whazoo.
Its a great place. I'll miss it dearly if'n I match at Iowa. Oh well, its only a 3 hour drive.
additionally, there's a large dose of "culture" within chicago. the Art Institute, the Field Museum of Natural History, the Shedd Aquarium, the Adler Planetarium, the Museum of Science & Industry, and more. there's also the Chicago Symphony Orchestra, the Lyric Opera, Steppenwolf, and 2nd City (where many SNL actors hail from).
Also located in Chicago is the interesting International Museum of Surgical Science as well as the ASA anesthesia museum which is in the suburbs. You can look them both up on their websites.
The Surgical Science museum is a nice short tour, 1/2 price for students and free parking in the back.