1861 ~ 1866
The Regiment itself was mustered into service on March 5, 1862 at Niles Michigan and left the state March 18th for St Louis Missouri. From there they moved to Pittsburgh Landing Tennessee where they were assigned to Colonel Peabody's Brigade of Prentiss' Division, Army of the Tennessee, arriving just in time for the battle of Shiloh. Part of the regiment was with Prentiss in the "Hornets Nest". Other engagements include:
Corinth MS, Iuka MS, Metamora TN, Middleburg TN, where they were complimented by General Grant in General Order No. 3 for gallant and efficient services on successfully defending their post against a force of 3000 Confederates under General Van Dorn, Mechanicsville MS, Siege of Vicksburg MS, Siege of Little Rock AR, Clarendon AR Devall's Bluff Gregory Landing AR, Bayou Fourche, Pine Bluff, Helena AR.
When mustered out, February 15, 1866, the 12th returned to Michigan arriving at Jackson on the 27th. At that time the unit was paid off and disbanded March 6, 1866. During their term of service the 12th had a total enrollment of 2357 men. Of these 29 were killed in action, 26 died of wounds, 17 died in confederate prisons, 316 died of disease and 221 were discharged for disabilities. This places the total Casualty Rate for the unit at 25.8%