The United States Border Patrol is a federal law enforcement agency within U.S. Customs and Border Protection (CBP), a component of the Department of Homeland Security (DHS). Its 16,000 agents are primarily responsible for immigration and border law enforcement as codified in the Immigration and Nationality Act. Their duty is to prevent terrorists and terrorist weapons from entering the United States and to deter, detect, and apprehend illegal immigrants and individuals involved in the illegal drug trade who enter the United States other than through designated ports of entry.

History

Mounted watchmen of the U.S. Immigration Service patrolled the border in an effort to prevent illegal crossings as early as 1904, but their efforts were irregular and undertaken only when resources permitted. The inspectors, usually called "mounted guards", operated out of El Paso, Texas. Though they never totaled more than seventy-five, they patrolled as far west as California trying to restrict the flow of illegal Chinese immigration.

In March 1915, Congress authorized a separate group of mounted guards, often referred to as "mounted inspectors". Most rode on horseback, but a few operated automobiles and boats. Although these inspectors had broader arrest authority, they still largely pursued Chinese immigrants trying to avoid the National Origins Act and Chinese Exclusion Act of 1882. These patrolmen were Immigrant Inspectors, assigned to inspection stations, and could not watch the border at all times. U.S. Army troops along the southwest border performed intermittent border patrolling, but this was secondary to "the more serious work of military training." Non-nationals encountered illegally in the U.S. by the army were directed to the immigration inspection stations. Texas Rangers were also sporadically assigned to patrol duties by the state, and their efforts were noted as "singularly effective".

The Border Patrol was founded on May 28, 1924 as an agency of the United States Department of Labor to prevent illegal entries along the Mexico–United States border. Additional operations were established along the Gulf Coast in 1927 to perform crewman control to insure that non-American crewmen departed on the same ship on which they arrived. Additional stations were temporarily added along the Gulf Coast, Florida and the Eastern Seaboard during the sixties when Cuba came under dictatorial control and entertained ideas of establishing USSR missile bases there.

Prior to 2003, the Border Patrol was part of the Immigration and Naturalization Service (INS), an agency that was within the U.S. Department of Justice. INS was disbanded in March 2003 when its operations were divided between CBP, United States Citizenship and Immigration Services, and U.S. Immigration and Customs Enforcement.

The priority mission of the Border Patrol, as a result of the 9/11 attacks and its merging into the Department of Homeland Security (DHS) is to prevent terrorists and terrorist weapons from entering the United States of America. However, the Border Patrol's traditional mission remains as the deterrence, detection and apprehension of illegal immigrants and individuals involved in the illegal drug trade who generally enter the United States other than through designated ports of entry.