Just a friendly warning or two...
I interviewed at Illinois last year, and the day was very, very long. The information session was a bit poorly planned. Several (and by several, I mean almost everyone) interviewees brought their parents, and the parents took up most of the seating. I had to stand for the whole thing, and in heels, that was a killer. The tour is also difficult on the feet, so bring some comfortable shoes with you. Also, parking was a nightmare, and be prepared to walk a good distance.
My interview was in the afternoon, and the info session was in the morning, so I went back to my hotel for a few hours to relax and "study" for my interview. There's not much to do in the interim if you stay on campus.
And finally, a blizzard hit the day of my interview, and I ended up snowed in for several days, because the roads were closed. So bring at least an extra set of clothing, and stay in a hotel that either has a restaurant or a "breakfast" area. The restaurants all closed, and we had no other access to food for the first 2 days. February is COLD in Illinois (it was like minus 5).
Best wishes to all of you!