The 88th Illinois Infantry Regiment was organized at Chicago on 27 August 1862 to serve three years[1] and mustered into federal service on 4 September 1862.

Chadbourne resigned on 14 October 1863 and was replaced as lieutenant colonel by Chandler, George W. Smith being promoted major.

[3] Chandler was killed in action on 27 June 1864[1] and was replaced as lieutenant colonel by Smith, Levi P. Holden being promoted major.

Captain John A. Bross was promoted lieutenant colonel of the 29th United States Colored Infantry Regiment on 6 April 1864.

[5] Captain Alexander C. McClurg was discharged on 28 June 1864 to accept a promotion to Assistant Adjutant General[1] in the XIV Corps.

The unit traveled to Covington, Kentucky, on 12 September and was attached to Colonel Nicholas Greusel's 1st Brigade, Brigadier General Gordon Granger's division, Army of the Ohio.

On 21 September, the regiment returned to Louisville where it was assigned to Greusel's 37th Brigade in Brigadier General Philip Sheridan's 11th Division.

[2] While marching in the evening of 4 October, the 88th Illinois began singing John Brown's Body and the entire division joined in.

This caused the 88th to momentarily waver, but its officers quickly rallied the men; they advanced a short distance and opened fire again.

[2] The pursuit of Bragg's army lasted until 16 October 1862, then the 88th Illinois marched to Nashville, Tennessee, reaching there on 7 November.

[18] After a terrified horde of rabbits hopped through their lines, the 88th Illinois rose up and opened fire on advancing Confederates at a range of 50 yd (46 m), forcing them back.

The unit served during the Tullahoma campaign from 24 June to 7 July and joined in the advance across the Tennessee River from 16 August to 22 September.

[14] The 88th Illinois under Lieutenant Colonel Chadbourne was attached to Brigadier General William Haines Lytle's 1st Brigade, Sheridan's 3rd Division, McCook's XX Corps, Rosecrans' Army of the Cumberland.

McCook overruled him and ordered an immediate attack, refusing Laiboldt's suggestion to arrange his regiments into line.

On Sheridan's front, the brigades were Brigadier General George D. Wagner, Colonel Charles Garrison Harker, and Sherman, left to right.

[14] In the Battle of Kennesaw Mountain on 27 June, Newton's division made the main IV Corps effort.

[1] During the Battle of Peachtree Creek on 20 July, the Confederates launched a major assault which first struck Newton's division and was repulsed.

[14] In September 1864, the 88th Illinois moved to Chattanooga, Whiteside, and Bridgeport, Tennessee, where it performed guard duty.

[33] When it became apparent that the Confederate army was mounting a mass assault, the commander of one of the advanced brigades begged Wagner to order a withdrawal, but was refused.

Consequently, the Confederate attackers routed Wagner's two brigades, and by closely following the fleeing soldiers, broke into the main Union defenses.

[34] Wagner's mob of fleeing Union soldiers, mixed with their Confederate pursuers, swept away Schofield's front-line units, creating a 200 yd (183 m) gap.

Because Opdycke's brigade recently had rearguard duty, all the men's rifled muskets were stacked loaded with the bayonets fixed.

Waving his cap, Lieutenant Colonel Smith galloped to the front of the combined 74th and 88th Illinois and led his men forward.

In a furious melee, Opdycke's soldiers battled their way through the Carter House buildings to occupy the second line of breastworks.

[36] On the first day, Elliott's division attacked after the Confederate defenses had been breached elsewhere and the skirmish line was able to capture the enemy position.

[37] On the second day, the soldiers of Wood's corps, seeing the left flank Confederate defenses collapse, attacked spontaneously and seized the line of breastworks in their front.

[38] After pursuing the defeated Confederate army, the 88th Illinois moved to Huntsville, Alabama, where it camped from January to March 1865.