And you can check out the results of past years' events here.
If you're an experienced player above USCF/FIDE 1900 and you care more about playing top-notch opponents than winning big cash prizes, you should seriously consider the Open Section. It's 9 rounds (which means that FIDE norms may be available, depending on your pairings), from May 27-31. Of course, if you have a 2700+ performance in the tournament, you could come home with $10,000! But I prefer to keep my expectations reasonable: I would be disappointed to score less than 3 points out of 9, and I'll be ecstatic if I score 4½ points.
Now if you care about chess and the chance to win up to $5,000, there are six strong class sections: Under 2100, Under 1900, Under 1700, Under 1500, and Under 1300. CCA makes reasonable efforts to keep overrated "sandbaggers" out of class sections, but please be aware that there's usually an underrated prodigy or two who you'll have to contend with. So please keep your expectations reasonable, and have fun playing chess!
In all of these sections, you can choose between 4-day, 3-day, and 2-day schedules. I strongly recommend playing in the 3-day or 4-day: young players in particular will learn much more at the slower time control. Young players (especially those close to the top of their section) should seriously consider playing up one section: a player rated 1510 will find the Under 1700 section challenging, but a 1650 player may want to opt for the Under 1900 section. For those mature enough to deal with losses, the experience of playing strong competition is worth more than the slim chance of winning big bucks. (For most players, however, playing up TWO sections is too much.)
Finally, the two-day Under 1000 section is ideal for beginners.
Please note that Illinois Chess Association membership is required for all Illinois residents! You can join ICA when you enter online here before May 24th!