The 126th New York Infantry was organized at Geneva, New York, and mustered in for three years service on August 22, 1862, under the command of Colonel Eliakim Sherrill.

The regiment was attached to Miles' Command, Harpers Ferry, Virginia, September 1862.

Camp Douglas, Chicago, Illinois, to December 1862.

3rd Brigade, Casey's Division, Defenses of Washington, D.C., to February 1863.

3rd Brigade, Casey's Division, XXII Corps, to April 1863.

3rd Brigade, Abercrombie's Division, XXII Corps, to June 1863.

3rd Brigade, 3rd Division, II Corps, Army of the Potomac, to March 1864.

Consolidated Brigade, 1st Division, II Corps, to November 1864.

Recruits and veterans were transferred to the 4th New York Heavy Artillery.

The regiment left New York for Baltimore, Maryland, then moved to Martinsburg, Virginia on September 2, 1862.

Paroled September 16 and sent to Annapolis, Maryland, then to Camp Douglas, Chicago, Illinois, and duty there guarding prisoners until November.

Battles of the Wilderness May 5–7; Spotsylvania May 8–12; Po River May 10; Spottsylvania Court House May 12–21.

Jerusalem Plank Road, Weldon Railroad, June 22–23, 1864.