He was born in 1816/17 (9 (44 in 1861), 10 (44 in 1861), 11 (47 in 1863)). He was born in Chester, Pennsylvania (9, 11).
When he enlisted, he was a carpenter, and was living in Philadelphia, Pennsylvania (9, 10, 11).
When he enlisted, he was 5 feet 10 inches tall, and had a light complexion, grey eyes, and light hair (9, 10, 11).
He enlisted and was mustered into service on 12 October 1861 (1) or 12 August [?] 1861 (9). (The Pennsylvania State Archives card has 12 November (10).) He was enlisted for three years, at Philadelphia, Pennsylvania, by Captain Sinex (9, 10). He was mustered in service as a private, in company F, by Captain Sinex (1, 9, 10, 15).
He was transferred to company D on 4 December 1861 (1, 12).
He was promoted to corporal when William Whitman died, on 18 June 1862 (8).
On 23 June 1863, he (along with three other men) was detailed to serve in the Provost Guard at Brigade Headquarters, and was ordered to report to Lieutenant William Walker, 146th New York Volunteers, who was the Brigade Provost Marshall (2).
He fought at the Battle of Gettysburg (14). He was then a corporal (14).
He reenlisted as a veteran volunteer, on 26 December 1863 (1, 10, 11). He was reenlisted for three years, at Bealton, Virginia, by Lieutenant Swan (11).
Effective 1 January 1864, he was promoted from corporal to fifth sergeant, replacing Mooney, who had been promoted (4, 7, 11).
On 10 March 1864, he was relieved from arrest and returned to duty (3).
On 9 July 1864, his sick leave was extended for two months (13).
On 17 January 1865, he went on a furlough, which expired on 27 January 1865 (6). He returned on 1 February 1865 (6).
On 3 July 1865, he was promoted to first sergeant, effective 1 July 1865 (1, 5, 10).
He mustered out on 10 July 1865 with his company (1, 10). He was orderly sergeant of company D (15).
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 special order 40, HQ 91st PA, 23 June 1863 (J W Thomas--but there is no J Thomas in company D)
3 regimental special order #19
4 special order 3, HQ 91st PA, 1 January 1864
5 special order 39, HQ 91st PA, 3 July 1865 (Isaac Thomas)
6 enlisted men's furloughs (Isaac Thomas)
7 company D, list of non-commissioned officers (Isaac W Thomas [in "reorganization" list])
8 company D, list of non-commissioned officers (Isaac W Thomas)
9 company D, descriptive roll, corporals, entry 4 (Isaac W Thomas)
10 Civil War Veterans' Card File, available at the Pennsylvania State Archives, searched 30 July 2004 (Isaac W Thomas)
11 company D, second descriptive roll, entry 4 (Isaac W Thomas)
12 company F, register of men transferred (Isaac W Thomas)
13 consolidated morning report, 91st PA, 13 July 1864 (Corpl [sic] Thomas)
14 Pennsylvania Memorial, Gettysburg, Pennsylvania (Isaac W Thomas)
15 index to compiled service records of volunteer Union soldiers who served in organizations from the state of Pennsylvania (Isaac W Thomas)