These are now mostly in the National Archives in Washington. The Customs Passenger Lists, dating from 1820, give only the country of origin. The Immigration Passenger Lists, from 1883, include details of the last place of residence. Depending on place or branch of service, these may specify the place, or at least the county of origin. These may in some cases, particularly for the marriages of recently arrived immigrants, include details the Irish place of origin of the persons recorded.
Most Catholic records are still in the parishes.
The records of other denominations may be held locally, or deposited with a variety of institutions, including public libraries, universities or diocesan archives.