Send U.S. citizenship applications to the local office of the United States Citizenship and Immigration Services, which can be found via the USCIS website. The necessary application forms are available on USCIS.gov.
Applicants for naturalized U.S. citizenship must be at least 18 years old, must possess permanent resident cards and must have been residents of the United States for at least five years, explains USCIS. The applicant must have lived in the state or district where her application was submitted for at least three months. In addition, all applicants must possess basic literacy in English and knowledge of U.S. history, be of good moral character, and be willing to take the oath of allegiance to the United States.