You don’t need the best eventing area when you are in college. Pick a good school and go on from there. Riding can be part of the decision (I picked my undergraduate institution in part because there was riding available on campus, but primarily because it is an excellent school). That said, I think there would be general agreement that the eventing hotspots in the United States are PA/MD/DE year around, Middleburg area year around, Aiken in the winter, Ocala in the winter, Temecula area in California (but a long distance to competitions other than those at Galway). Here are some Universities (not knowing how competitive a school you want or can get into, what area of studies interests you, or what else may play a role in your decision).
University of Florida (close to Ocala, etc). Maxxtrot is in Williston and could give you more information
University of Virginia - there are many trainers and barns in Charlottesville now
University of Delaware, University of Pennsylvania - close (UDel) and functional (UPenn) proximity to the Unionville evening barns. UPenn also gives you the option of Radnor area barns.
Washington and Lee - close to the Virginia Horse Park and other private stables
University of Kentucky - close to the Kentucky Horse Park with many good training and boarding options
University of Central Florida - up and coming with some areas of excellence. Near www.ashmoreequestrian.com which has a small xc facility on property and is BHS credentialed (I board and ride there some winters)
Vanderbilt - Nashville. Eponacowgirl is fairly close to Nashville and could tell you more. This is a top University
Pepperdine - would put you in the fabulous Malibu and is close enough to http://www.pepperwoodridingcenter.com/prc_ContactInfo.html that I would guess there are riding opportunities
Shenandoah University - doable for Middleburg area boarding/riding and Middleburg is a huge eventing area
University of South Carolina - about an hour from Aiken, but there is some stuff closer to Columbia
University of North Carolina/Duke/Wake Forest/Elon - Doug Payne has a new farm not too far and you are striking distance of Southern Pines for weekends
UNC Charlotte relatively close to Bonnie Mosser and to Lesley Stevenson