A homeport is defined as the city and state where a sea-going vessel is customarily kept. It may be the port where the vessel is registered or enrolled. State laws vary, but the registration of a vessel for domestic trade is typically made at its homeport, while registration of a vessel for overseas trade may be required to be made at a central office.
The following is an example of one state's guidelines for census residency reporting:
"Crews of military vessels with a U.S. homeport - Counted at their usual onshore residence if they report one (the place where they live and sleep most of the time when they are onshore) or otherwise at their vessel's homeport."