With the aid of naturalization records, family historians can trace the life stories of individuals and groups. This database is an index to naturalization petition cards originally compiled by the New York County Supreme Court (in Manhattan) between 1907 and 1924. Each entry provides the applicant's name, address, date the card was filed, and reference information for the file location. Many records include whether the naturalization was "cancelled" or "denied" for the individual. It contains the names of over 136,000 individuals. For researchers of immigrant ancestors who may have applied for naturalization in Manhattan, this can be a useful source of information.

Since colonial times, New York County was limited to Manhattan, and until 1898 it was the only county in New York City. These records represent only Manhattan, though there may be records from sections of Westchester County added to New York County (they became Bronx County in 1914).

The following books are great resources for information on naturalization records: They Became Americans: Finding Naturalization Records and Ethnic Origins by Loretto Dennis Szucs, Printed Sources: A Guide to Published Genealogical Records edited by Kory L Meyerink, and The Source: A Guidebook of American Genealogy by Loretto Dennis Szucs.