Researchers have long used census records as a tool in naturalization research, for two reasons. First, early 20th century census records asked for each person’s citizenship status. If the subject of research consistently claimed to be a naturalized citizen decade after decade, or if they suddenly claimed to be naturalized ten years after claiming to be an alien, researchers could make assumptions regarding whether a naturalization record existed.
Second, census records allow researchers to track ancestors who moved from place to place. Except in certain instances, immigrants had to naturalize in a court with jurisdiction over their residence. Census records show where someone lived, hence they hold clues to the court where someone may have naturalized.
However, census records contain many errors regarding citizenship status. The vast majority of such errors involved people who mistakenly believed themselves to be naturalized. Many wrongly thought they became citizens through a parent’s naturalization, or through military service. Others believed they were a citizen after filing a Declaration of Intention (1st papers). Researchers must also remember that the individual named in a census record is not always the person who provided the information shown. The data found in a census record may have come from the immigrant’s next door neighbor, who provided his best guess in answer to all questions about the immigrant.