On July 1, 1899, "The Porto Rico Regiment of Infantry, United States Army" was created. On July 1, 1901 Lieutenant Colonel James Anderson Buchanan commanded the regiment. He was later promoted to Colonel on July 21, 1902 and to Brigadier General in 1905. Buchanan served in Puerto Rico from 1898 to 1903. The military installation, Fort Buchanan, was named after Brigadier General James A. Buchanan, first commander of the Puerto Rico Regiment.
     The Puerto Rico Regiment approved by Congress on May 27, 1908 was officially designated as the 65th Infantry Regiment in 1920, after defending the Canal Zone during World War I. A tract of 300 acres approximately six miles on the south shore of San Juan Bay was acquired to provide the regiment with a training area. The site was established in 1923 as Camp Buchanan. It served as a target range and maneuver area for Army and National Guard troops from 1923 to 1939.
     In May 1940 the location was designated as Fort Buchanan and expanded initially to 1,514 and later to 4,500 acres. During World War II, Fort Buchanan housed a depot supplying the Army Antilles Department. It also processed local troops through its replacement center. The industrial complex included pier facilities, ammunition storage areas and an extensive railroad network connecting the military installation to the bay.
     Puerto Rican Soldiers were deployed for WW II and Korea from the train station located where the Golf Club is presently located, to the rail-connected Army terminal by the bay. At the time, Fort Buchanan served as a citizens training camp and soldier processing station. After WW II the post was gradually reduced to its current 756 acres.
Fort Buchanan remained a command depot with post facilities, a personnel center, and a special training center until closure as an Army post in 1966. On December 31, 1966, with the deactivation of the Antilles Command, Fort Buchanan came under the U.S. Navy control.
     In December 1971 Fort Buchanan returned to U.S. Army control under Third US Army. On July 1, 1973 Fort Buchanan came under direct control of Forces Command (FORSCOM).
Following the Department of Defense Unified Command Plan, Fort Buchanan came under control of U.S. Southern Command (SOUTHCOM), and on August 13, 1999 became the home of US Army South (USARSO), which subsequently departed in 2003.
     On October 1, 2002 Fort Buchanan became part of the Southeast Regional Office of the Installation Management Agency (IMA). On October 1, 2003, Fort Buchanan became an IMA Reserve installation. Later, on October 1, 2006 Fort Buchanan became a Garrison under Installation Management Command, Southeast Region (IMCOM-SE).
     October 1, 2008 the Commanding General of the 81st Regional Readiness Command became Fort Buchanan's Senior Mission Commander under the U.S. Army Reserve Command. Based on December 2008 Unified Command Plan, Fort Buchanan falls under the U.S. Northern Command (USNORTHCOM) area of operations.
     U.S. Army Garrison Fort Buchanan consists of 756 acres (including Las Colinas and Coconut Grove family housing) with a real estate value estimated at $1.2 billion dollars. It serves a population of approximately 130,000 among veterans, retirees, civilians, military personnel and their dependents in Puerto Rico, Virgin Islands and Latin America.
     Fort Buchanan is host to a number of tenant activities, such as: the 1st Mission Support Command, the U.S. Army Reserve major tenant unit, other Reserve and Puerto Rico National Guard components, Navy Reserve, Marine Reserve, Army/Air Force Exchange Services (AAFES), Defense Commissary Agency (DECA), Rodriguez Army Health Clinic (RAHC), Veterinarian Clinic, Defense Military Pay Office (DMPO), Defense Contracting Audit Agency, TRICARE, Community Based Warriors in Transition Unit (CBWTU), Civilian Personnel Advisory Center (CPAC), Military Entrance Processing Station (MEPS), among others.
     Fort Buchanan also hosts a number of non-DoD organizations that provide valuable services to Soldiers, their dependents and community members, such as: Pentagon Federal Credit Union, Banco Popular de Puerto Rico, U.S. Postal Service, AAFES Concessionaires and the U.S. Customs and Border Patrol.
     As directed by the Chief of the Army Reserve, Fort Buchanan's island wide support mission consists of providing real property management and base operations support for all Army Reserve assets in Puerto Rico and the Virgin Islands. Also, on a reimbursable basis, when requested, provide support to the Puerto Rico National Guard and other reserve components of other services.
     Fort Buchanan supports readiness and mission execution, providing quality services and facilities, optimizing resources, sustaining the environment and enhancing the well-being of the community. It conducts its mission sustained by seven directorates; Human Resources, Family and Morale, Welfare and Recreation; Plans, Training, Mobilization and Security; Emergency Services, Logistics, Public Works and Information Management; seven support offices - Legal, Public Affairs, Religious Support, Equal Employment Opportunity, Safety, Internal Review and Contracting; and three management and control offices - Resource Management; Plans, Analysis and Integration; and the Administrative Office.
     Among the factors that make U.S. Army Garrison Fort Buchanan unique are: its key and strategic location providing fast and cost-effective support to missions in the Caribbean, Central and South America area or responsibility; its Hispanic cultural ties with Latin America; and its significant role as host of "joint" sister services reserve components representing the U.S. Armed Forces in Puerto Rico.