Subsequently, the unit moved to Bird's Point, Missouri from which Companies A and B participated in an expedition to Little River on 22–23 June.

[3] The reorganized 11th Illinois Infantry Regiment was mustered into Federal service for a three-year enlistment on 30 July 1861, at Cairo.

Nevius was replaced as colonel by James Henry Coates who received a brevet promotion to brigadier general on 13 March 1865.

[6] Ransom was wounded four times and rose to command the Left Wing of the XVI Corps in the Atlanta campaign, but died of poor health on 29 October 1864.

Captain Charles T. Hotchkiss was promoted lieutenant colonel of the 89th Illinois Infantry Regiment on 4 September 1862.

[4] Major Smith D. Atkins resigned on 17 April 1862 and was promoted colonel of the 92nd Illinois Infantry Regiment on 4 September 1862.

[3] At the Battle of Fort Donelson on 15 February 1862, the 11th Illinois led by Lieutenant Colonel Ransom (who was wounded) was part of Colonel Wallace's 2nd Brigade, Brigadier General John Alexander McClernand's 1st Division, under the overall command of Brigadier General Ulysses S.

[3] At the Battle of Shiloh on 6–7 April 1862, the 11th Illinois was attached to Colonel C. Carroll Marsh's 2nd Brigade, McClernand's 1st Division, in Major General Grant's Army of the Tennessee.

[14] On the first day, McClernand ordered Marsh to move his brigade to support Brigadier General William Tecumseh Sherman's division.

After first moving to Sherman's right rear, Marsh shifted farther to the left and deployed the 11th, 20th, 45th, and 48th Illinois Infantry Regiments.

When Marsh's brigade rallied on a new defense line near Jones Field, a portion of the 70th Ohio Infantry Regiment joined the 11th Illinois and fought with it the rest of the day.

At 12:30 pm, Marsh's brigade joined a counterattack by Sherman and McClernand and the 11th and 20th Illinois overran a Confederate Kentucky battery.

Ransom was bleeding from a head wound, but continued to lead the regiment until his horse was killed; then he went to the rear.

The regiment joined an expedition from Fort Donelson to Clarksville, Tennessee, from 5–10 September that resulted in the Battle of Riggins Hill.

[19] In this action, Colonel William Warren Lowe led 1,100 Union troops from the 11th Illinois, 71st Ohio, and 13th Wisconsin Infantry Regiments, the 5th Iowa Cavalry Regiment, and Battery C and Battery H, 2nd Illinois Light Artillery to disperse a force of 700 Confederates that occupied Clarksville.

[1] The 11th Illinois was attached to the 2nd Brigade, 6th Division, Left Wing XIII Corps, Army of the Tennessee in November–December 1862.

[1] On 20–24 November 1862, the regiment moved to La Grange, Tennessee, where it joined the 6th Division under Brigadier General John McArthur.

[3] At Vicksburg, the 11th Illinois was assigned to Ransom's 2nd Brigade, McArthur's 6th Division, Major General James B. McPherson's XVII Corps, Grant's Army of the Tennessee.

In the Battle of Yazoo City on 5 March, the unit sustained losses of 1 officer and 8 enlisted men killed, 24 wounded, and 12 missing.

The force was accompanied by five gunboats under Captain Elias K. Owen and later joined by 250 troopers from the 1st Mississippi Cavalry Regiment (African).

The attackers surrounded nine companies of the 11th Illinois under Major McKee and 80 men of the 1st Mississippi in rifle pits outside the town, while forcing their way into the streets.

Brigadier General Lawrence Sullivan Ross tried three times to bluff McKee into surrendering, but that officer refused to capitulate.

On 1–7 July, the regiment was part of Major General Henry Warner Slocum's expedition to Jackson, Mississippi, where it fought in three actions.

[22] From this time until December 1864, the 11th Illinois was part of the 1st Brigade, 2nd Division, XIX Corps, Army of the Gulf.

From February to July 1865, the regiment was attached to the 2nd Brigade, 1st Division, XIII Corps, Army of West Mississippi.

[25] Fort Blakeley had 3,500 Confederate defenders and 33 guns under Brigadier General St. John Richardson Liddell.

[27] Veatch assigned Dennis' brigade to lead the attack with one regiment deployed as skirmishers and the other two forming the assault column.

The regiment was mustered out of service on 14 July at Baton Rouge, and traveled to Springfield, Illinois, for final payment and discharge.