The 125th Infantry was one of the 41 regiments authorized by Congress during the Civil War. There were four African American units, two in the south and two on the western frontier.
The 125th Infantry was organized in Spring 1865 in Louisville, KY. The enlistees had to commit to three years of service. During August 1866, eight companies of the 125th were transferred to Mexico and remained there until they were replaced between September and December of 1867. The eight companies were the first African American troops to serve at Ft. Selden.
The 125th was eventually sent to Fort Riley, KS where the men were discharged; the 125th Infantry was disbanded December 20, 1867.
For more see The Buffalo Soldiers: a narrative of the Negro Cavalry in the West, by W. H. Leckie.