The Illinois and Minnesota volunteers joined the Eighth Missouri because their home state's quota for enlistments was full.
[4] The regiment's first commander was Col. Morgan Lewis Smith, a New Yorker who had moved west to Missouri after serving as an enlisted man in the Regular Army.
After a two-month-long campaign, it was the first regiment to enter the strategic rail center of Corinth, Mississippi, following the Confederate evacuation in May 1862, and in late December, it took part in the Battle of Chickasaw Bayou.
The 8th Missouri saw considerable service in the Battle of Vicksburg, where eleven men of the regiment won the Medal of Honor in one day during the May 22, 1863, assault on Stockade Redan.
Those who remained on active duty were consolidated into a battalion of two companies, and as such participated in the rest of the Atlanta Campaign and Sherman's March to the Sea.