The Eleventh left the State June 24, 1861, and in less than a month was engaged at First Bull Run; its loss, as then officially reported, was 8 killed, 40 wounded, and 40 missing. In the campaigns of 1862, it served in Grover's (1st) Brigade, Hooker's (2d) Division, Third Corps. At Williamsburg it lost 7 killed, 59 wounded, and 1 missing; at Manassas, 9 killed, 79 wounded, and 25 missing; at Gettysburg, 23 killed, 96 wounded, and 10 missing -- fully half of those engaged. Lt.-Col. George P. Tileston was killed at Manassas, and Colonel Blaisdell fell at Petersburg, June 23, 1864, while in command of a brigade. At Gettysburg, the division was commanded by Humphreys, the brigade by Carr (J. B.), and the regiment by Lt.-Col. Porter D. Tripp, the command fighting on the Emmettsburg Road. The Eleventh was transferred in March, 1864, to Brewster's (2d) Brigade, Mott's (4th) Division, Second Corps, in which it fought at the Wilderness, where it lost 9 killed, 54 wounded, and 12 missing. Its term of service expired on June 12, 1864, when the original members were mustered out. The recruits and reenlisted veterans left in the field were formed into a battalion of five companies, designated the Eleventh Battalion, which was subsequently increased by two companies of similar material left by the Sixteenth Massachusetts.