John G. Dean was 18 years old and working as farmer in Portland when he enlisted on Sept. 3, 1862 as a private and was mustered into the 6th Battery of the 1st Maine Light Artillery on Sept. 18. Deane was promoted to Corporal on Nov. 13, 1862, to Sergeant in Oct. 1863, and to 2nd Lieutenant on July 1, 1864. Deane was an enlisted man for most of his service. On Oct. 14, 1864 he was appointed as an Assistant Aide De Camp on the Staff of Chief of Artillery, to Major John G. Hagland at the Head Quarters, Artillery Brigade of the 2nd Army Corps. On Dec. 30, 1864, he requested his first leave of absence in order to go to Portland, Maine to purchase a house for his mother. Dean was Mustered Out on June 17, 1865 at Augusta, ME.
Dean was described as having blue eye, light hair, light complexion and a height of 5’ 7”.