The bands, the crowds, the patriotic fervor of late April soon give way to war's harshest reality: death. The first man to die was William Choates of C company, who passed away on July 1, 1861, not amidst the glories of battle but in the throes of fever. He was buried near Camp Blair, and is presumably buried there still.
The regiment's baptism into war came less than three weeks later in the action at Blackburn's Ford on July 18, 1861, a prelude to the first battle of Bull Run on July 21. The Third suffered its first wartime casualty early on Saturday morning, July 20, 1861, when Homer Morgan of B company allegedly took his own life.
The Third Michigan infantry covered the retreat of the federal troops from Bull Run on July 21, and subsequently went into a succession of camps around Washington throughout the fall and winter of 1861-62. The regiment participated in McClellan's Peninsular campaign of 1862 and suffered its worst casualties to date at Fair Oaks, Virginia on May 31, 1862 and at Groveton (or Second Bull Run) on August 29, 1862.
The Third Michigan infantry played a peripheral part in the battle of Fredericksburg on December 13, 1862. The next major action for the regiment was at Chancellorsville, Virginia, on May 3, 1863, followed by Gettysburg where the Third found itself exposed in the Peach Orchard on July 2, 1863.
Near the end of the summer of 1863 the Third Michigan was detached to the Department of the East under General Dix and sent northward to New York City in late August to serve as a deterrent to the expected rioting in the upcoming draft in that state. The Regiment spent several days in New York City, the draft went off without event and the Third Michigan was sent up the Hudson River to Troy to oversee the draft in that city, where it remained for two weeks before it returned south to rejoin the Army of the Potomac.
By early May of 1864, the Army of the Potomac was again on the move in Virginia and the Third Michigan was hotly engaged on May 5-6 at the Wilderness and on May 11-12 at Spotsylvania Court House. The Regiment participated in Grant's sidestepping moves southeastward around Lee's right flank across the North Anna river and ended its military service in the trenches in front of Petersburg, Virginia, on June 10, 1864, and was formally mustered out that same day.
Those men who had enlisted in June of 1861 but who had not reenlisted were sent home to be mustered out in Detroit on June 20,1864, while the remainder of the regiment, reenlisted veterans and recent enlistees, were incorporated into four companies (A, E, F, and I) and then consolidated into the Fifth Michigan infantry.
The history of the Regiment as an integral component of the Union military structure was over, but its history as a relic of that conflict, as a symbol of what that struggle represented would continue to linger on in the guise of the Old Third Michigan Association until well into the twentieth century, indeed until every member had passed away.