The 23rd New York Infantry Regiment was a Union Army infantry regiment which was active from 10 May 1861 to 22 May 1863 during the American Civil War. The regiment was organized in Elmira, Chemung County, New York, and it was nicknamed the "Southern Tier Regiment" for recruiting in the Southern Tier of Western New York. The regiment was attached to the Army of the Potomac, and it first saw major action at the Second Battle of Bull Run before fighting at the Battle of South Mountain, the Battle of Antietam, the Battle of Fredericksburg, and the Battle of Chancellorsville before being mustered out in 1863.