Some of the lists in the National Archives date back to 1798, but the majority date from 1820, when federal law made them mandatory, or later. Those over 50 years old have been copied on microfilm and can be consulted by genealogists. Transcripts of arrivals between October 1, 1819, and September 30, 1820, and between September 1821 and December 1823 can also be found in two printed volumes, issued by the Genealogical Publishing Company and the Magna Carta Book Company, respectively.
The surviving passenger lists, which contain many gaps, are for arrivals at Atlantic and Gulf of Mexico ports. Fires in 1851 and 1940 destroyed San Francisco's arrival lists, and those of other Pacific ports, if they exist, have never been transferred to the National Archives. Fortunately, Louis J. Rasmussen's San Francisco Ship Passenger Lists–four volumes of lists reconstructed from newspaper announcements–covers passenger arrivals from the beginning of 1850 through January 1853, a period of intense migration into California as a result of the discovery of gold there in 1848.
Passenger arrival lists exist in two major groups: Customs Passenger Lists and Immigration Passenger Lists. The Customs Passenger Lists, so called because they were first filed with the collectors of customs, include each passenger's name, age, sex and occupation; the name of the vessel on which he sailed; the port of embarkation and the port and date of entry.
The Immigration Passenger Lists–which recorded information about visitors to this country and Americans returning from abroad, as well as actual immigrants–are especially valuable. In addition to the information listed in the Custom Passenger Lists, they include the passenger's place of birth and last place of residence. After 1893 they include the name and address of an American relative of the immigrant, and after 1907 the name and address of the passenger's nearest relative in his homeland.
Unfortunately, the passenger lists are arranged chronologically, and indexes are scarce, In order to find an ancestor in the unindexed Customs Passenger Lists a researcher needs to know his or her name, the port through which he or she entered this country and either the name of the vessel and its approximate date of arrival or the name of the port from which it sailed and the exact date of arrival. To locate an ancestor in the Immigration Passenger Lists, the researcher needs to know his or her name and age, the port of entry, the name of the vessel and the date of its arrival.
It's possible to located an ancestor knowing only the port of entry and the year of arrival. Indexes, which are on microfilm in the National Archives and some libraries, primarily cover the years 1820 to 1846, while most of the lists of arrivals from 1846 until after the turn of the century remain unindexed.
Consulting the records of vessel entrances maintained at ports and now housed at the National Archives will help when a researcher has only partial information. These give the names of ships, their dates of arrival in various ports and the countries from which they sailed. A researcher can make a general search of all the passenger arrival lists for a particular port, but the sheer size of this undertaking makes it a course of last resort. Knowing the port from which an ancestor sailed is a great help.