Ahh, I just looked it up, it's by port, not by state. So each municipality can register boats. That's a bit confusing, most jurisdictions (here in Canada, Europe, some other places I know of) require unique names. It could be quite hazardous to have two vessels answering to the same call in some circumstances, so I'm a bit surprised the US is so lax in this regard. (imagine a hypothetical, two boats named "Leo from Seattle" one is sinking, and loses radio contact, the Coast Guard comes out and contacts "Leo from Seattle" who says, "No, we're fine, no need for help here." CG turns back for home while the other "Leo from Seattle"'s crew drowns).
From the US Coast Guard:
"Documented vessels do not display their official numbers on the outside of the hull, but are identified by the name and hailing port. The application for documentation must include a name for the vessel composed of letters of the Latin alphabet or Arabic or Roman numerals and may not exceed 33 characters. The name may not be identical, actually or phonetically, to any word or words used to solicit assistance at sea; may not contain or be phonetically identical to obscene, indecent, or profane language, or to racial or ethnic epithets. Once established, a vessel's name may not be changed without application, fees, and the consent of the Director, National Vessel Documentation Center. There is no rule against duplication of names for documented vessels, so hailing ports are helpful in identifying vessels."