Found two soldiers from each side listed as Thomas G. King. Doesn't mean one of them is your Thomas G. King. He could have mustered as simply " Thomas King " or " T.G. King." Knowing where he lived in the 1860 census would be a good start. The Georgia soldier I've listed may be the same man with records in two different units.

Glenn

The Union soldiers :

King, Thomas G.

REGIMENT NAME:15th Regiment, Maine Infantry
SIDE:Union:
COMPANY:K
SOLDIER'S RANK IN:Private
SOLDIER'S RANK OUT:Private

King, Thomas G.

REGIMENT NAME:14th Regiment, Michigan Infantry
SIDE:Union:
COMPANY:B
SOLDIER'S RANK IN:Private
SOLDIER'S RANK OUT:Private

The Confederates :

King, Thomas G.

REGIMENT NAME:8th Regiment, Georgia Infantry (State Guards)
SIDE:Confederate
COMPANY:D
SOLDIER'S RANK IN:Private
SOLDIER'S RANK OUT:Private

King, Thomas G.

REGIMENT NAME:55th Regiment, Georgia Infantry
SIDE:Confederate
COMPANY:B
SOLDIER'S RANK IN:Corporal
SOLDIER'S RANK OUT:Corporal