I was accepted here but will not be on the Chicago campus. Is there a difference between campuses as far as curriculum goes? And also, a basic question, what is the difference between UIC and the University of Illinois? I know this is a dumb question but its confusing to me... I will be in Champaign mixed in with undergrads but do I go to UIC or U of I?
TickTock spelt it out pretty good.
As far as the differences between Urbana, Rockford, and Peoria, you should base your decision on learning style and location.
Everyone does M1 in Urbana, so the main difference is the M2 lectures and the M3 and M4 clinical experience. You will be on a campus with undergrads, in a building that is shared with undergrads, but your classes will be medical students only. You definitely feel more part of the UIUC campus than you feel part of UIC (even though that's technically who does your registration, financial aid, etc.)
Urbana is at the U of I main campus. You will do your M1 year there, so you will get a general feel for the city no matter where you wind up doing M2-M4. Champaign-Urbana is definitely a place that caters to the younger crowd moreso than the other two cities. It's great if you want to have fun. Unfortunately you won't have much time for that, especially during your M2 and M3 year. As far as the M2 year, Urbana notoriously has the fewest lecture hours, usually starting at 8am and finishing around 11am or noon. If you are an independent learner, this will be most useful for you.
Rockford is a medium-sized city an hour's drive from the western suburbs of Chicago. They also have a more relaxed approach to the M2 lectures, and they have one half-day per week devoted to clinical experience during M2 year, which is a unique aspect about their campus. You can expect to spend 8am-noon or 1pm in lecture on an average day in Rockford. They also allow their M4 students to do as many away rotations as they want.
Peoria is a medium-sized city in the west central Illinois valley that is 3 hours from both Chicago and St. Louis. Peoria takes a much more aggressive approach to the M2 year, and students can expect to spend 8am-3pm in lecture on a given day, and sometimes it can be as late as 5pm. This approach is good if you want more communication with lecturers. While Peoria curriculum does cover some information that is not on the USMLE Step 1 exam, the extra hours spent in lecture is mostly repeating content. For instance, you may have a lecture on Crohn's disease from a pathologist and then subsequently a lecture on Crohn's disease from a gastroenterologist. Obviously you'll get a very different perspective from those two doctors. Peoria M4 students are required to spend 16 of their 36 weeks in Peoria and the other 20 can be away rotations. From what I've seen, however, Peoria has the best hospitals (including a brand new Children's hospital)..
In my honest opinion, in retrospect, if I had to do it again, I would have stayed in Urbana-Champaign. M2 year in Peoria was very stressful and it was very difficult to stay caught up. I felt like we were required to learn a lot of information that was neither useful for Step 1 or the clinical years (or at least that would be remembered that long). I would have appreciated the shorter hours and more time to really solidify the fundamentals on my own, rather than learning about how to read a echocardiogram (there's plenty of time to do that M3-M4 years). I don't feel my colleagues in Rockford or Urbana are any less prepared because they had fewer lecture hours. Champaign is a much more modernized city than Rockford and Peoria, and there is much more to do there.
Anyway, that's my two cents..
I'm nervous for you! My meeting will be next month. AHHH! 
