The Trans-Mississippi Department, also known as the Trans-Mississippi Theater or Trans-Mississippi District, was the Confederate military designation for the geographic area of operations west of the Mississippi River during the American Civil War.

The Department was formed in May of 1862 and consisted of the states of Arkansas, Missouri, Texas, Indian Territory, and those portions of the State of Louisiana that were west of the Mississippi.

Trans-Mississippi Commanders

• Brigadier General Paul O. Hebert - (18 June 1862 - 31 May 1862)
• Major General Thomas C. Hindman - (31 May 1862 - 30 July 1862)
• Major General Theophilus H. Holmes - (30 July 1862 - 7 March 1863)
• Lieutenant General Edmund Kirby Smith - (7 March 1863 - 19 April 1865)
• Lieutenant General Simon Bolivar Buckner, Sr. - (19 April 1865 - 22 April 1865)
• General Edmund Kirby Smith - (22 April 1865 - 26 May 1865)