Upon the signing of the Treaty of Paris on December 10, 1898, Spain ceded Puerto Rico to the Congress of the United States.

A tract of 300 acres (120 ha) approximately 6 miles (9.7 km) on the south shore of San Juan Bay was acquired to provide the regiment with a training area.

[citation needed] United States Army Garrison Fort Buchanan consists of 746.16 acres (301.96 ha) between the municipalities of Bayamón and Guaynabo, Puerto Rico with a real estate value estimated at $560 million.

Fort Buchanan serves a population of approximately 130,000, including military personnel, their dependents, retirees, veterans, and the civilian workforce.

Fort Buchanan also hosts a number of non-DoD organizations that provide services to soldiers, their dependents, and community members, including the Pentagon Federal Credit Union PenFed, Banco Popular de Puerto Rico, and AAFES Concessionaires.

Fort Buchanan also provides support to United States Department of Homeland Security agencies such as the U.S. Customs and Border Protection.

The Puerto Rico Army National Guard Recruiting and Retention Division (R&R Div), the 480th Military Police Company and the Medical Section Cell C59.

The United States Marine Corps Reserve relocated the Detachment 1, Landing Support Company, Combat Logistics Regiment 45 into this facility.

The Fort Buchanan Armed Forces Reserve Center serves about 400 personnel on a rotating basis, with a maximum of 250 members per weekend.

This facility was named after senior civilian aide to the secretary of the Army for Puerto Rico Major General (Ret) Felix A. Santoni.

The Puerto Rico National Guard will posthumously name this Readiness Center at Fort Buchanan after Korean War Veteran and former member of the 65th Infantry Regiment and Medal of Honor recipient Master Sergeant Juan E. Negrón.