Can my offer of admission be rescinded if I accepted admission at another school?

I was accepted to U of I and UIC. In order, to graduate early my high school nearly forced me to pick one on the spot in December. I accepted admission at UIC, and I may still go there but if at some point before May 1st I decide that I don’t want to go to UIC and I’d rather go to U of I, would that offer still be on the table?

No. But you should not accept two admission offer at the same time. Did you pay the deposit already? I think that is silly to force a student to pay the deposit before the final decision is made.

Are you in one of the Chicago area schools where the district is requiring that all students have a job offer or a college admission before graduation?

You should have until the standard reply date to accept admissions at U of I. Just stay in touch with admissions there to make certain that they have received all the documents necessary. Make certain that they get a copy of your final transcript from your high school.

If you do choose U of I over UIC, you need to let UIC know. You probably will lose any deposits you have made to UIC.

If you haven’t told U of I you don’t want to go there, then the offer is still there.
You would need to tell UIUC that you don’t want to attend (possibly lose any deposit you have made) and then accept U of I.
After May 1 you should only have one college you have told that you are going to attend.
Before that, it is okay to have multiple offers on the table (even if you have chosen one).