I graduated from Cornell College in '90. Great college, the "One Class at a Time" makes all the difference in the world. I wish more places would do that. Just a great great way to take classes (though difficult for things like math or sciences). I can't say enough good things about this MUCH lower stress but easily just as (if not more) educationally effective method of going to college. It's very very cool.
At the end of every block you get block break, and there will certainly be some good parties. Potentially Wednesday after your final, and even Thurs, Fri, and Sat. You can get a month's worth of parties in over block break, never party on a school night, and still have Sunday to recover.
Beyond the normal college drinking/partying, and/or if you aren't a drinker/partyer (I'm not) there's not a lot going on in Mt Vernon. If you can get access to a car you can (as mentioned above) hit Cedar Rapids or (more likely) Iowa City. With UofI in Iowa City there's ALWAYS something going on there: parties, concerts, shopping, gaming, etc. I saw Miles Davis there, it was awesome. I saw Stevie Ray Vaughn in CR or Iowa City as well (best concert I've ever seen). I think it's actually a pretty good exchange: you get easy access to all the activities in two active metropolitan areas (I don't think either is more than a 20 minute drive) but you don't have to deal with the hassles of a large university or that same metro area.
Don't ignore Palisades State Park for a some good peaceful nature hiking or picnics. The Pal is a really pretty place, though not terribly big. There are other Parks as well, they would certainly be worth checking out.
I wouldn't worry a bit about a screamo band, unless you don't have a car. I would bet Iowa City is filled to the gills with college screamo bands with turnover. It's just a matter of getting there.
A car is the key obviously, but if you do have a car, or even a friend/roommate that has a car and similar interests or will let you borrow the car (how I did it for three years), all you need to do is stay aware of what's going on in Iowa City and CR and you'll have no shortage of fun things to do.
It's probably a lot easier to keep track of that stuff now, when I was there we had no internet!