What seems obvious isn’t always true. Vermont actually has 80% of freshman from out of state.
Private colleges are often more diverse geographically, but less than you might think as the interactive graphic The Chronicle for Higher Education created a few years ago: https://www.chronicle.com/interactives/freshmen_insts#id=130794 (This isn’t working for me now, you may need to be a subscriber, but the link will show you Yale.)