- February 1862
- October 26, 1862
- On November 9, 1861, the United States War Department issued General Orders No. 97, which divided the Western Department into the Department of New Mexico, the Department of the Ohio, the Department of Western Virginia, and the Department of the Missouri. The directive appointed Major General Henry Halleck as commander of the latter.
- In February 1862, Major General Henry Halleck organized the Union troops operating in the State of Missouri, creating the Army of the Mississippi.
- Brigadier General John Pope commanded the Army of the Mississippi from February 23, 1862, to June 26, 1862.
- At its largest, the Army of the Mississippi consisted of roughly 25,000 soldiers.
- On March 14, 1862, the Army of the Mississippi forced the withdrawal of Confederate troops from New Madrid to Island No. 10 on the Mississippi River.
- Then, with the assistance of Flag Officer Andrew Hull Foote’s naval forces, the Army of the Mississippi subdued the Confederate garrison on Island No. 10 on April 7, 1862, taking nearly 7,000 prisoners, while suffering fewer than 100 casualties.
- The Army of the Mississippi participated in the Siege of Corinth from April 29 to May 30, 1862, serving on the extreme left of Major general Henry Halleck’s Union army.
- Brigadier General William S. Rosecrans commanded the Army of the Mississippi from June 26 to October 24, 1862.
- Bolstered by two divisions of the Army of West Tennessee, the Army of the Mississippi participated in the Union victory at Battle of Iuka (September 19, 1862.
- Bolstered by two divisions of the Army of West Tennessee, the Army of the Mississippi successfully defended the town of Corinth, Mississippi from a Confederate attack at the Second Battle of Corinth on October 3 and 4, 1862.
- On October 26, 1862, Major General Ulysses S. Grant, commanding Department of the Tennessee, issued General orders No. 2, stating “The army heretofore known as the ‘Army of the Mississippi,’ being now divided and in different Departments, will be discontinued as a separate Army.”.