The Army of the Trans-Mississippi was a major Confederate army under the Department of the Trans-Mississippi during the American Civil War. It was the last major Confederate command to surrender, submitting on May 26, 1865, exactly one month after General Johnston had surrendered in the eastern United States.
The Department of the Trans-Mississippi separated from the Western Department of the Confederacy on May 26, 1862. It consisted primarily of the three Confederate states west of the Mississippi (Texas, Louisiana, and Arkansas), the contested state of Missouri, and two Confederate territories - the Indian Territory and Confederate Arizona (roughly corresponding to the present-day states of Oklahoma, New Mexico, and Arizona). The command of the area was given to Major-General T. H. Holmes. The Trans-Mississippi was the operational theater for many quasi-independent forces, including Quantrill's Raiders and the Missouri Bushwhackers.
The Army of the Trans-Mississippi originally numbered well over 50,000 troops, but fewer than 43,000 were available by the end of the war. Major campaigns included Sibley's New Mexico campaign, Banks' Red River campaign, and Price's Missouri campaign. The last battle of the Civil War, the Battle of Palmito Ranch, was fought May 12–13, 1865, by units of the Army of the Trans-Mississippi.
General E. Kirby Smith, who commanded the Army, surrendered to Union forces on May 26, 1865, although by that point many of his troops had already deserted. The last remaining Army of the Trans-Mississippi force – and also the last remaining Confederate force – was the 1st Cherokee Mounted Rifles, commanded by Brigadier-General Stand Watie. Watie surrendered on June 23.
- Trans-Mississippi Army, I Corps (Headquartered at Shreveport, Department of Louisiana)
- Trans-Mississippi Army, II Corps (Department of Arkansas and Missouri)
- Trans-Mississippi Army, III Corps (Headquartered at Galveston, Department of Texas)
- Trans-Mississippi Army, Cavalry Corps
- Trans-Mississippi Army, Reserve Corps
- The Reserve Corps was established on September 10, 1864, to support the Trans-Mississippi Army.
- Symonds, Craig L. (1992). Joseph E. Johnston: A Civil War Biography. New York: W. W. Norton. ISBN 9780393311303.
- "Southern Army- Trans-Mississippi Army". Civil War Home. March 28, 2004. Archived from the original on December 12, 2013.
- Eicher, John H. (2001). Civil War High Commands. Stanford University Press. pp. 891–892. ISBN 0804736413.
- "REBEL TRANS-MISSISSIPPI ARMY.; Strength of the Rebels What they are Doing Affairs in Texas, & c. Forrest and Dick Taylor Whipped". The New York Times. April 9, 1865.
- Clampitt, Brad R. (May 2001). The Break-up of the Confederate Trans-Mississippi Army, 1865. University of North Texas Press.