TheDepartment of the West, later known as theWestern Department, was a major command (Department) of theUnited States Army during the 19th century. It oversaw the military affairs in the country west of theMississippi River to the borders ofCalifornia andOregon.

The Department of the West was created in a reform of army organization nationwide on October 31, 1853, from a consolidation of the existing6th Military District (headquartered atJefferson Barracks, Missouri) and7th Military District (Fort Smith, Arkansas) Departments. It reported directly to the headquarters of the Army inWashington, D.C. In the 1853 reorganization theDepartment of the Pacific was also created, from consolidation of the 10th (California) and 11th (Oregon) Departments. The Department of the West's headquarters continued at Jefferson Barracks inSt. Louis, although it moved briefly toFort Leavenworth, Kansas, during theBleeding Kansas skirmishes.

As the Southern states were seceding, just before theAmerican Civil War began, the department was organized to include the country west of the Mississippi River and east of theRocky Mountains, except forTexas,Utah Territory, andNew Mexico Territory, includingMissouri,Arkansas,Iowa,Minnesota,Kansas Territory (the state ofKansas after January 29, 1861),Nebraska Territory,Colorado Territory (after February 28, 1861),Dakota Territory (after March 2, 1861),Indian Territory (later the state ofOklahoma), andLouisiana west of the Mississippi River. On June 6, 1861, Missouri was transferred to theDepartment of the Ohio.

On July 31, 1861, the Department of the West was merged into the Western Department ofMaj. Gen.John C. Frémont. The Western Department, which had been organized on July 3, 1861, also included Missouri and Illinois from the Department of the Ohio and New Mexico Territory from the Department of New Mexico. Western Kentucky was added from the Department of Kentucky on August 15, 1861. Frémont was relieved by Maj. Gen.David Hunter under the orders ofPresidentAbraham Lincoln, contingent upon the circumstance that Frémont did not lead an army into battle by October 24, 1861. The Western Department was discontinued on November 9, 1861, with New Mexico Territory being transferred back to theDepartment of New Mexico, and the rest being divided between theDepartments of Missouri andKansas.^[1]

Department commanders were:^[2]

Department of the West

Western Department

• Army of the West (1846)
• Department of the Pacific
• Department of the Missouri

• Eicher, John H., & Eicher, David J.,Civil War High Commands, Stanford University Press, 2001,ISBN 0-8047-3641-3.
• Military History at rootsweb.com

• Departments and districts of the United States Army
• Union army departments
• 1853 establishments in the United States

• Articles with short description
• Short description matches Wikidata