You might want to look at Loren Pope’s books “Colleges that Change Lives” and “Looking Beyond the Ivy League” (don’t pay attention to the latter title). Colleges that Change Lives also has a website and national fairs. Some of the schools mentioned above are in CTCL list.
Just to second or fourth or whatever the schools mentioned above: Lawrence, Oberlin, Grinnell, College of Wooster, maybe Kenyon or Macalaster-? I believe U. of Colorado has good composition department. Northwestern and U. of Chicago do too, at least at the grad level.
Spirit Manager’s post cautioning you about doing a BA at a school that offers a BM or has had music school/conservatory is a good warning, but as she said, look into the details at each school. If you are a composer, you want to have opportunities to have your music played by good musicians: at some schools you can also make some of your own opportunities.
A general BA music major is fine for composition and should leave room for other interests as well. Check out the details of major requirements and, especially, distribution requirements. Also, for composition, you might want to listen to faculty (and even student) works because the aesthestic can vary quite a bit. This becomes an essential part of grad school choice but is somewhat relevant at the undergrad level too. The course listings will also give clues.
Are you familiar with “new music” and 20th/21st century composers?