Originally called the Army Corps of Central Kentucky, it was created in the fall of 1861 as a subsection of Department No.

2 (Western Department) was created on June 25, 1861, under the command of Maj. Gen. Leonidas Polk, and had military jurisdiction and control over parts of Alabama, Tennessee, Arkansas, Mississippi, and Louisiana.

On September 2, 1861, the department was expanded to include all of Arkansas and military operations in the state of Missouri, and then on September 10 the area was expanded again to include all of Arkansas, Tennessee, more of Mississippi, and all military operations in Kansas, Kentucky, Missouri, and any Indian territories rallying to the Confederate cause west of Arkansas and Missouri.

After being exchanged in August 1862, Buckner was promoted to major general and commanded a division with these same forces in the Army of Mississippi under the leadership of Gen. Braxton Bragg.

The area of operation for this army was designated as the part of Tennessee north of the Cumberland River and that part of Kentucky west of where the Cumberland River entered Tennessee to the east.