Before 9/11, the Immigration and Naturalization Service (INS) was responsible for enforcing immigration law. After 9/11, the Homeland Security Act of 2002 abolished the INS and created the Department of Homeland Security (DHS). The statute transferred primary responsibility for enforcing and administering immigration laws from the Attorney General to the Secretary of the DHS. Today, three separate agencies within DHS handle immigration functions. USCIS administers benefits and services; law enforcement responsibilities are shared by ICE and CBP.
Department of Homeland Security:
Department of Health & Human Services, Administration for Children and Families: