Central Index System

Overview
The Department of Homeland Security U.S. Citizenship and Immigration Services maintains the Central Index System (CIS), a database system originally developed by the legacy Immigration and Naturalization Service. CIS contains information on the status of 57 million applicants/petitioners seeking immigration benefits to include: lawful permanent residents, naturalized citizens, U.S. border crossers, aliens who illegally entered the United States, aliens who have been issued employment authorization documents, individuals who petitioned for benefits on behalf of family members, and other individuals subject to the provisions of the Immigration and Nationality Act (INA).

Source
[Department of Homeland Security]], Privacy Impact Assessment for the Central Index System (June 22, 2007) (full-text).