He was 38 years old when he was enlisted (3). He was born in Warren, New Jersey (3).
He was a carpe[nter] (3).
He was 5 feet 8 inches tall, and had a light complexion, blue eyes, and light hair (3).
He was enlisted and mustered into service on 15 September 1861 (1, 3). He served as a private in company D (1).
He fought at the Battle of Gettysburg (4).
He reenlisted as a veteran volunteer (1).
He died on 7 March 1864 (1, 2).
1 Bates, Samuel Penniman. History of Pennsylvania volunteers, 1861-5. Harrisburg: B. Singerly, state printer, 1869-71. 5 volumes. 'Ninety-first regiment', volume 3, pages 186-233. (In the roster)
2 company D, register of deaths (Mathias Kirkoff)
3 company D, descriptive roll, entry 13 (Mathias Kirkoff)
4 Pennsylvania Memorial, Gettysburg, Pennsylvania (Mathias Kirkoff)
[I did not find an entry from him in the index on <www.ancestry.com> to the pension index by names]