When we joined SB Nation, I started going through the archives on blogs like this one, trying to find out what our new bunkmates thought of USF athletics. One thing I noticed almost every time USF came up on The Smoking Musket was that no one could figure out why our school was the University of South Florida when Tampa is not in south Florida.
So Charley and everyone, here's your answer. As far as I can tell there are four main reasons.
1. The name "University of Tampa" was taken.
2. Florida looked a lot different 50 years ago. Once you got south of Tampa and St. Petersburg, there wasn't very much civilization until you got to Miami and Fort Lauderdale. You could reasonably consider Tampa part of south Florida because not that many people lived in the real south Florida. No one would do that now with the population explosion in places like Sarasota, Fort Myers, and Naples (which went from about 15,000 residents in 1960 to over 250,000 in 2000, and it's probably even higher now).
3. When USF was founded, it was the southernmost public university in Florida. The University of Miami already existed as a private school, but the only three public schools were Florida (in Gainesville), Florida State (in Tallahassee), and Florida A&M (also in Tallahassee).
It's all perspective. If most of the population and all the public schools are in the northern part of Florida, and you're a politician sitting in Tallahassee trying to name this school, then Tampa's going to look pretty south to you, especially when there's not much out there beyond it.
To make USF look even more badly named in hindsight, the state built a bunch of new public schools in the 1960s, and gave them all sensible names. They were placed in Jacksonville (North Florida), Orlando (Central Florida), Boca Raton (Florida Atlantic), Miami (Florida International), and Pensacola (West Florida). Later, two of USF's satellite campuses broke off into their own universities -- New College in Sarasota, and Florida Gulf Coast University in Fort Myers.
4. It was the best of a bad group of names. I found this story in the Google newspaper archive from April 26, 1970 -- it's from the St. Petersburg TImes and it's a sidebar about how USF got its name. Get a load of some of the crap they came up with and had the good sense to reject.
See, I disagree with that last paragraph. The name is really a matter of great importance, because there's NO FREAKING WAY we're in the Big East with a name like Sunshine State University. I think they banish you to Division III for a stupid name like that.
There you go -- that's why it's South Florida. It looks dumb now, but like that drunken Taco Bell run at 1:30 in the morning, it made sense at the time.