The monument to the 1st Massachusetts Cavalry Regiment is south of Gettysburg on Sedgwick Avenue. (39.796061 N, 77.234161 W; Google map; Tour map: Sedgwick Avenue) It was erected in 1885 by the Commonwealth of Massachusetts.
The 1st Massachusetts Cavalry was commanded at the Battle of Gettysburg by Lieutenant Colonel Greely S. Curtis. It brought 292 men to the field, and suffered no losses. The regiment was temporarily attached to the 6th Corps Headquarters.
From the monument:
First Mass. Cavalry
2nd Cavalry Division
on detached service
See more on the First Massachusetts Cavalry Regiment during the Civil War