There are many Magical communities in America, shared with Muggles. St. Simons Island, Georgia, a small island off the southern cost of Georgia, for example, ahs a large wizarding population, myself included. It's neighboring town, Brunswick, is also home to many magical folk, and many Muggle borns go to chool for the first ten years of their lives at the local elementary schools. 

In New York,much like Diagon Alley in London, is a small area only accessible to Witches and Wizards, called Liberty Way. In order to get into it, you must go down a street very close to Rockefeller center, whisper the password to a mannequin ('Reichstart') and you would be well on your way to the area.