I am from Alabama and will be attending a school in Illinois this fall. I’ve been assuming that class attire is Nike shorts, chacos, and a (sometimes, but not always large) t shirt. I know that most people attending school in Alabama wear this to class, but is this normal in other states/schools?
Pretty much anything
Doesn’t really matter as long as it’s not ridiculously inappropriate.
People generally don’t care what you wear to class, especially if you are going to a larger state school with large lecture classes. Wear what you are comfortable with
Whatever you’re comfortable in as long as it isn’t a distraction. 
You’re thinking MUCH too hard about this.
Wear whatever you feel like wearing. I dress for the weather more than anything. When things started warming up this spring, I just wore comfortable t-shirts and shorts if applicable. I have a large collection of American Eagle shirts, so go figure.
The “large t-shirt” deal is more suited to sorority girls. Don’t worry so much about what everyone else is wearing and dress for YOURSELF–the most important part.
Also, there’s a HUGE divide about the acceptability of Chacos at my university. So no, I don’t think it’s what everyone is wearing. 
But again, wear it if it’s what your heart desires.
Whatever your’s choice.
Four years from now, you will be amused at your even asking this question.
College is a time to learn to not follow and to not care what others think about you, but instead to be an independent thinker.
Wear whatever you choose.
Use your common sense and dress for the northerly weather, as it gets cool by September, and downright frigid in winter. Yes, everyone says you can wear whatever you want, but once you get on campus, you will get a feel for the campus culture. If this matters to you, then yes, there is a regional difference as to how kids tend to dress. Personally, I think it’s up to you.
Yoga pants on yoga pants on yoga pants on yoga pants.
YogaPants
^^^
Franklin D. Roosevelt having a great love for yoga pants made me giggle.
Pretty much whatever you feel like wearing. There’s no dress code or “acceptable attire” list at most colleges.
My biggest concern is offending a professor by walking into class wearing the outfit I described above. My school doesn’t have a dress code so it’s not like I’ll be breaking any rules by wearing shorts to class. I just didn’t know if professors will feel like I’m not taking a class seriously if I wear shorts and t-shirts. Once it gets colder I will probably swap over to jeans and closed toe shoes. Yoga pants aren’t really my style unless I’m wearing shorts over them 
I can guarantee you that your professor doesn’t care what you’re wearing, as long as it’s not some grossly inappropriate outfit. I’ve rarely worn anything but jeans or shorts and t-shirts to my classes. I’m pretty sure every professor I’ve ever had has taken me quite seriously. Odds are they won’t even notice what you’re wearing.
So long as you don’t look like you’re out clubbing in Atlantic City, you aren’t gonna offend anyone with your attire.
Just don’t go stark naked or in a Speedo.
As an Illinois native, I strongly advise you to get a VERY warm coat and snow boots- Sorrel boots are great and don’t look too clunky. You’ll be able to wear shorts and a t-shirt maybe a few weeks out of the year, depending on your tolerance for cold and the start/end date of your college. Illinois is very snowy and windy, so get lots of warm sweaters and outerwear.
From what I know, the Nike shorts/big T-shirt look is a very “Southern sorority girl” kind of thing, whether for stylistic or practical reasons, I don’t know. Good luck in those winters! I don’t miss them one bit
If you’re taking a lab you might be required to wear closed toe shoes.
Unless your school has a strict dress code (i.e. Bob Jones), anything should be allowed as long as the important parts are covered, laws are followed, and you don’t have anything extremely offensive on your clothing.
Some professors may take you more seriously if you come dressed modestly, but if you are in a class with hundreds of other students, chances are you won’t stand out enough for them to care either way.
College is not high school, no one cares what you wear.