[1] The 1st Massachusetts Cavalry was organized at Camp Brigham in Readville, Massachusetts beginning September 3, 1861 and mustered in under the command of Colonel Robert Williams.
Attached to Pleasanton's Cavalry, Army of the Potomac, to October 1862.
Averill's Brigade, Cavalry Division, Army of the Potomac, to January 1863.
1st Brigade, 2nd Division, Cavalry Corps, Army of the Potomac, to April 1865.
The 1st Massachusetts Cavalry mustered out of service on June 29, 1865 and was discharged at Readville on July 24, 1865.