He was born in 1817/18 (2 (43 in 1861), 5 (44 in 1861)).
He enlisted and was mustered into service, at Philadelphia, Pennsylvania, on 19 November 1861 (1, 2, 4 (6 Nov 61)). He was a private in company B (1, 3, 4, 6).
He deserted on 10 December 1861 (1, 2). He was a private, in company B (3, 4 [not on the muster-out roll], 6).
Bates (4) has another John McCormick mustered in on 6 November 1861, in company K, but they were different ages when they enrolled according to the Pennsylvania Archives cards (5). The index to compiled service records (3) indicates that a John and William are the same person; it is possible that I've linked the wrong John to William.
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) (William McCormick)
2 Civil War Veterans' Card File, available at the Pennsylvania State Archives, searched 28 June 2004 (Wm McCormick)
3 index to compiled service records of volunteer Union soldiers who served in organizations from the state of Pennsylvania (William McCormick)
4 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) (John McCormick)
5 Civil War Veterans' Card File, available at the Pennsylvania State Archives, searched 28 June 2004 (John McCormick)
6 index to compiled service records of volunteer Union soldiers who served in organizations from the state of Pennsylvania (John McCormick)