Naturalization is the process by which U.S. citizenship is granted to a foreign citizen or national after he or she fulfills the requirements established by Congress and the U.S. Citizenship and Immigration Services (formerly, the Immigration and Naturalization Service). Naturalization was typically a 3-step process: (1) the Declaration of Intention (“First Papers”), which could be filed by an immigrant at any time after their arrival in the U.S., (2) the Petition for Naturalization (“Second Papers” or “Final Papers”), which could be filed by the immigrant after 5 years of residency in the U.S. and from 2-7 years after they filed their declaration, and (3) the Certificate of Naturalization, which was issued by the court in which the petition was filed and marked the official granting of U.S. citizenship. The declaration of intention and the petition for naturalization often contain valuable information for genealogy research. If filed after 1906, they are likely to include a specific town of origin, date, ship, and port of arrival in the U.S., marital status and date of marriage, names, birthdates, and birthplaces of spouse and children, and present and last foreign address. If an immigrant changed their name sometime between their arrival in the U.S. and the time of their naturalization, their original name may also have been recorded. Please note that the names of an immigrant’s parents are not regularly found associated with naturalization records.
Foreign-born women (prior to 1922) and children typically did not file applications for naturalization, because their naturalization status was determined by that of the head of their household. In other words, women automatically became citizens if they married a U.S. citizen or if their husband naturalized while they were married; similarly, children automatically became citizens if their father naturalized while they were minors. There was no paperwork created when a person naturalized through derivative naturalization.
The process by which our ancestors could become American citizens substantially evolved over the course of the 20th century. Thus, it is helpful to provide a brief timeline of U.S. naturalization laws.
Prior to September 27, 1906: For most of our nation’s history, naturalizations could take place in any court - federal, state, county, or city - and each court kept its own records. Procedures were not standardized and forms required only minimal personal information, typically the applicant’s name, country of origin, date of application, and, sometimes, date and port of arrival.
September 27, 1906: The Basic Naturalization Act took effect, and the federal Immigration and Naturalization Service (INS) was established. Procedures became more standardized and new forms requiring significantly more personal information (see "U.S. Naturalization Records" section above) came into use. Local and state courts were required to forward naturalization papers to the INS.
September 22, 1922: Congress passed the Married Women's Citizenship Act (the Cable Act) and women were now required to apply for citizenship on their own.
July 1, 1929: An amendment to the Basic Naturalization Act, which granted women and children who had derived citizenship from their husband or father the option to apply for a certificate of derivative citizenship, took effect. Declarations of intention and certificates now included a photograph of the applicant.
December 24, 1952: The Immigration and Nationality Act took effect, which made the declaration of intention voluntary.
FamilySearch provides an overview of the history of naturalization.