Slice, the pizza blog, has a good roundup of US regional pizza styles, tracing the hereditary links between different styles as different groups of Italian immigrants spread across the nation.
(My favorite slice? Hands down, no question, absolutely Massimo's on College Street in Toronto, a slice so good that I don't think I've ever eaten a slice of pizza one tenth as delicious, nothing even in the running. Truly in a league of its own. My mouth just flooded with saliva as I typed those words, and I'm presently 6,000 miles from Massimo's)
Variations, I believe, are found throughout the Midwest–from Ohio to Milwaukee to Chicago to wherever. I'd even go so far as to say that the "Chicago-style" pizza just above is really a variation of "Midwest-style." The Midwest style is round, thin, very crisp yet tender-flaky, and is party- or tavern-cut into the grid. Sauces and topping preference may differ from city to city and region to region, but this style seems to crop up often in the heartland.
(Image: Spanish Chorizo Pizza, a Creative Commons Attribution ShareAlike licensed photo from Avlxyz's Flickr stream)