The 164th New York was one of the four regiments recruited in the fall of 1862 of Irish-Americans for a brigade to be known as the Corcoran Legion. It was organized by the famed Brigadier General Michael Corcoran, formerly of the 69th New York State Militia. Corcoran however, died when his horse fell on him in December of 1863, so his brigade and the 164th fought without him. The Legion and the 164th was assigned to Gibbon's Second Corps of the Army of the Potomac in May of 1864, in time to join Grant's bloody march on Richmond. The regiment's first significant action was at Spotsylvania in May, but it was the assault at Cold Harbor that resulted in its major casualties of the war with six officers in addition to Colonel McMahon killed, 16 enlisted men dead, 59 wounded and 82 missing. The regiment would again have significant casualties in attacks on Petersburg in June of the same year. The 164th was mustered out on July 15, 1865 after having gone through some of the bloodiest fights of the Army of the Potomac. Though issued Hawkin's Zouave pattern uniforms by the Government, their fezzes were topped off with green tassels as a visible Irish distinction.