The monument to the 33rd Massachusetts is southeast of Gettysburg on Slocum Avenue (39.819861° N, 77.226149° W; Google map; Tour map: Stevens Knoll) It was dedicated in 1885 by the State of Massachusetts.

Monument to the 33rd Massachusetts infantry at Gettyburg

The regiment was commanded at Gettysburg by Colonel Adin B. Underwood. It brought 562 men to the field.

11th Corps Headquarters Flag 11C-2D

From the tablet on the front of the monument:

The Thirty Third Massachusetts Infantry
Detached from the Second Brigade, Second Division, Eleventh Corps on July 2nd, 1863. After supporting the batteries in action on  Cemetery Hill, while in position in a line extending westward from near this spot, withstood and assisted in repulsing a charge of the enemy’s infantry in its front. Loss in the battle eight killed, thirty six wounded.