50 States. Numerous territories. I don't know why people only mention Puerto Rico, because there is also Wake Island, Guam, U.S. Virgin Islands, American Samoa, Northern Mariana Islands, ...so basically a bunch of islands. Though only those born on Guam, Puerto Rico, Northern Mariana Islands, and the U.S. Virgin Islands gain U.S. citizenship by birth. Idk why those on Wake Island and American Samoa don't, though they can apply for citizenship and are never turned down...which means its a bunch of paperwork for nothing really but whatevs...