The 173rd New York Infantry Regiment (a.k.a., "4th Metropolitan Guard" and "4th National Guard") was an infantry regiment in the Union Army during the American Civil War.
The 173rd New York Infantry was organized at Brooklyn, New York beginning September 22, 1862 and mustered in for three-years service November 10, 1862 under the command of Colonel Charles B. Morton.
The regiment was attached to Grover's Division, Department of the Gulf, to January 1863.
2nd Brigade, 3rd Division, XIX Corps, Department of the Gulf, to September 1863.
3rd Brigade, Dwight's Division, Department of Washington, to June 1865.
District of Savannah, Georgia, Department of the South, to October 1865.
Occupation of Baton Rouge, Louisiana, December 17, 1862, and duty there until March 1863.
Operations on Bayou Plaquemine and the Black and Atchafalaya Rivers February 18–28.
Served with the brigade, detached as supply train guard for the army, from August 14 to October 27.
Duty near Middletown and Newtown until December, and at Stevenson's Depot and Winchester until April 1865.