Department of the West
The Department of the West, later known as the Western Department, was a major command of the United States Army during the 19th century. It oversaw the military affairs in the country west of the Mississippi River to the borders of California and Oregon.
Organization
The Department of the West was created in a reform of army organization nationwide on October 31, 1853, from a consolidation of the existing 6th Military District and 7th Military District Departments. It reported directly to the headquarters of the Army in Washington, D.C. In the 1853 reorganization the Department of the Pacific was also created, from consolidation of the 10th and 11th Departments. The Department of the West's headquarters continued at Jefferson Barracks in St. Louis, although it moved briefly to Fort Leavenworth, Kansas, during the Bleeding Kansas skirmishes.Civil War
As the Southern states were seceding, just before the American Civil War began, the department was organized to include the country west of the Mississippi River and east of the Rocky Mountains, except for Texas, Utah Territory, and New Mexico Territory, including Missouri, Arkansas, Iowa, Minnesota, Kansas Territory, Nebraska Territory, Colorado Territory, Dakota Territory, Indian Territory, and Louisiana west of the Mississippi River. On June 6, 1861, Missouri was transferred to the Department of the Ohio.Western Department
On July 31, 1861, the Department of the West was merged into the Western Department of Maj. 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 of President Abraham 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 the Department of New Mexico, and the rest being divided between the Departments of Missouri and Kansas.Command history
Department commanders were:Department of the West
| Commander | From | To |
| Newman S. Clarke | ||
| David E. Twiggs | ||
| Persifor F. Smith | ||
| Brig. Gen. William S. Harney | November 10, 1860 | April 23, 1861 |
| Captain Nathaniel Lyon | April 23, 1861 | April 29, 1861 |
| Colonel Edmund B. Alexander | April 29, 1861 | May 11, 1861 |
| Brig. Gen. William S. Harney | May 11, 1861 | May 31, 1861 |
| Brig. Gen. Nathaniel Lyon | May 31, 1861 | July 3, 1861 |
Western Department
| Commander | From | To |
| Brig. Gen. Nathaniel Lyon | July 3, 1861 | July 25, 1861 |
| Maj. Gen. John C. Frémont | July 3, 1861 | October 24, 1861 |
| Maj. Gen. David Hunter | October 24, 1861 | November 9, 1861 |