The 156th New York Infantry Regiment (aka, "Mountain Legion") was an infantry regiment in the Union Army during the American Civil War.

The 156th New York Infantry was organized at Kingston, New York beginning August 23, 1862 and mustered in for three-years service on November 17, 1862 under the command of Colonel Erastus Cooke.

The regiment was attached to Sherman's Division, Department of the Gulf, to January 1863.

1st Brigade, 3rd Division, XIX Corps, Department of the Gulf, January 1863.

2nd Brigade, 1st Division, XIX Corps, to February 1864.

3rd Brigade, 2nd Division, XIX Corps, Department of the Gulf, to July 1864, and Army of the Shenandoah, Middle Military Division, to January 1865.

3rd Brigade, Grover's Division, District of Savannah, Georgia, Department of the South, to March 1865.

The 156th New York Infantry mustered out of service October 23, 1865 at Augusta, Georgia.

Moved to Baton Rouge, then to Donaldsonville, July 11–15, and duty there until August 15.

Moved to Savannah, Ga., January 5–22, and duty there until March 5.