This regiment was organized by Col. Henry W. Slocum at Elmira, New York, and accepted by the State on May 21, 1861.

The regiment mustered June 15, 1861, and left New York for Washington, D.C., on July 10, 1861.

They were attached to Porter's Brigade, Hunter's Division, McDowell's Army of Northeast Virginia until August 1910.

Next they were attached to Heintzelman's Brigade, Division of the Potomac, to October 1861.

White Oak Swamp and Glendale June 30.

In works at Centreville August 28–31, and cover Pope's retreat to Fairfax Court House September 1.

Three years' men transferred to 121st Regiment New York Infantry.

[2] Regiment lost during service 2 Officers and 72 Enlisted men killed and mortally wounded and 2 Officers and 70 Enlisted men by disease.

[2] The 27th New York Volunteer Infantry Regiment was reformed following the Civil War to replace the 3rd New York Volunteer Infantry Regiment that was disbanded.