I know that UIUC is huge, but my understanding has always been that it was extremely difficult to gain admission to. Northern Illinois, Iowa and Purdue are filled with kids that couldn't get in...
UIUC published stats for 2022[1]: 1 in 4 for engineering and business (roughly top-50 university odds), 1 in 15 for computer science (roughly top-10 university odds), a coin flip or better for most other majors. General admit seems pretty relaxed at 44.8%.
[1] https://www.admissions.illinois.edu/apply/freshman/admit-rat...