Is Indiana University or the University of Illinois more selective for undergraduate admissions?

The biggest practical tradeoff is that the University of Illinois is typically the tougher admit overall, especially for certain majors, while Indiana University is less selective at the university-wide level and a bit more predictable for many applicants. At Illinois, admission can vary a lot by college and program, with engineering, computer science, and some business pathways standing out as especially competitive. Indiana also has selective options, particularly Kelley and a few direct-admit tracks, but the campus as a whole is usually more accessible than UIUC.

So if you are asking the broad question of which school is more selective for undergraduate admission, the clearer answer is the University of Illinois. That is the case most students and counselors would recognize, and it shows up most strongly in the level of competition for high-demand majors. Illinois tends to attract a very large pool of academically strong applicants, including many aiming at programs with limited space.

The part that causes confusion is that these schools are not equally selective across every major. At Indiana, a student applying to the general university may face a different level of difficulty than someone trying for Kelley direct admission. At Illinois, the gap between a less selective major and something like engineering or CS can be even bigger, so two applicants to the same university can have very different odds.

In short, for undergraduate admissions overall, Illinois is more selective than Indiana. Indiana is still a respected Big Ten university, and some of its programs are quite competitive, but if you want the head-to-head answer on general selectivity, Illinois is the harder school to get into.