Thomas O’Hearn was born in 1847, in Ohio, the son of Irish natives Dominic O’Hearn (b. 1819-1898) and Margaret Horan (b. 1830).
Dominic and Margaret left Ireland and by 1847 had settled in Ohio. Between 1851 and 1855 the family moved to Michigan. By 1860 Thomas was attending school with his younger siblings in Tallmadge, Ottawa County.
Thomas stood 5’9” with blue eyes, light hair and a light complexion and was 18 years old and probably working as a farmer in Muskegon County or perhaps in Tallmadge, Ottawa County when he enlisted in Company E on February 8, 1864, at Grand Rapids for 3 years, crediting Muskegon, Muskegon County, and was mustered the same day. He joined the Regiment on March 27, and was quite possibly wounded in early May of 1864.
He was transferred to Company E, 5th Michigan Infantry upon consolidation of the 3rd and 5th Michigan Regiments on June 10, 1864, and was either killed in action on June 16, 1864, near Petersburg, Virginia, or he may have died on July 16, 1864, from wounds received near Petersburg (or perhaps in early May). In any case, he was presumably among the unknown soldiers interred in Petersburg National Cemetery.
In June of 1897 his mother Margaret was still living in Michigan when she applied for a dependent’s pension (no. 656903) but the certificate was never granted. His family was still living in Tallmadge, Ottawa County in 1870.