United States historical military districts

U.S. military administration districts, departments, divisions.
These entities were sometimes the only governmental authority in the listed areas, although they often co-existed with civil governments in scarcely populated states and territories.
1800–1813
From May 14, 1800, the army was divided into 11 geographical districts, with an informal alignment into western and eastern departments. On February 15, 1809, the Army was reorganized into Northern, Southern, and Western Military Districts. In June 1810, the Southern and Western Districts were consolidated as the Southern Department, and the Northern District was designated Northern Department.
1813–1815
On March 19, 1813, during the War of 1812 the United States was divided into 9 numbered military districts. They were increased to 10 on July 2, 1814 and reduced to 9 by consolidation of the 4th and 10th Districts in January 1815.
1815–1821
On May 17, 1815, the military districts were abolished, and superseded by 10 numbered Military Departments, divided equally between the Division of the North with 1st–5th Military Departments and Division of the South with the 6th–10th Military Departments.
1821–37
In May 1821, the Divisions of the North and South and the Military Departments were abolished and the Army reorganized into Eastern and Western Departments. From time to time various departments or Armies appeared in the Western Department.
1837–1844
In 1837 the Army returned to a system of Divisions with subordinate numbered Military departments. Between 1842 and 1844, the Divisions were abolished with only the Military Departments in operation. 
1844–1848
In 1844 the Army renewed the use of the Eastern and Western Divisions during the Mexican–American War.
1848–1853
Following the Mexican war, the army reorganized to occupy the vast new territory acquired.
1853–1861
After October 31, 1853 the division echelon was eliminated and the departments in the east became one Department of the East, administering all the territory east of the Mississippi River. The six western departments consolidated into four (Departments of Texas, New Mexico, the West, and the Pacific). The system returned to six departments in 1858 when the Department of Utah was created in January, and the Department of the Pacific split into the Departments of California and Oregon in September.
Eastern United States
Western United States
Pacific area
1861–1865
During the American Civil War the Eastern Department was eliminated, exploding into many Departments, districts and subdistricts of the Union Army.
1865-1881
Eastern United States
Southeastern United States
Western United States
Pacific area