As an expansion on my earlier post, besides Mizzou (probably Illinois’ best rivalry, given the setup in St. Louis), I would say I have or have had a “historically speaking dislike” for the following teams:
Indiana: Have had a very even and intense series with them over the years, and it’s cool that two states so into basketball (college and high school) border each other. It’s kind of ebbed and flowed, though - it was red hot during the ‘80s with Knight and Henson publicly feuding and some classic games, and it got really big again during the Eric Gordon saga, but not as intense lately.
Iowa: This was big before I was born (Bruce Pearl is still public enemy #1 in IL), but it totally fell off in the late ‘90s and for most of the time since 2000. However, this actually turned into a great rivalry again a few years ago. There was so much intensity when we played the last few years and no shortage of bad blood.
Northwestern: Meh, it’s just not that easy to hate NU. For most of my life, I actively rooted for them as that “little engine that could,” lol. However, I’ll admit that their “Chicago’s Big Ten Team” campaign got under my skin and added some decent fuel to this series for a bit. However, they have started to be pretty bad again, and we lead the all-time series 141-42, including winning 7 in a row … it’s just not a great series and inspires very subdued hate.
North Carolina: I was indeed bitter when they beat us in the National Championship in 2005. I still think the 2005 Illini were not just one of the best teams to never win it all, but one of the best college basketball teams of all-time; there have been multiple National Champions since 2005 who I think the ‘05 Illini would beat by 10+. For that to be just another NC for North Carolina and a depressing, missed opportunity for us sucked. Illinois wins that game, and their history as a program is thought of in the same breath as Arizona or Syracuse (look at the stats and add 1 NC…), but now we retain the dubious honor of being one of (if not) the best programs to have never won it all. However, as time has passed, I don’t see UNC any differently than any other Blue Blood.
Out of fellow B1G schools, I’m surprised/disappointed that a better rivalry has never developed with Wisconsin. The Bears/Packers overlap is obvious, and the states have no lost love for each other. I think that since 2000, Wisconsin and Illinois are the winningest Big Ten programs after MSU, too, so we have had a lot of meaningful battles.