The War Department, to ease command and control of the Army as it operated across the country, divided the United States into military departments in the early 1850s. This map, created in 1869 by the Office of the Chief of Engineers in the War Department, identifies the various military departments throughout the United States. A general officer or senior colonel commanded each department. These commanders were responsible for the administration of the department as well as the operations in the field.
National Archives, Records of the Office of the Chief of Engineers