During the American Civil War, the United States Army had reorganized, including the new Department of the Pacific which was created on January 15, 1861. By 1863, the department had five districts, including the District of Southern California established on September 25, 1861. It was composed of San Luis Obispo County, Tulare County, Santa Barbara County, Los Angeles County, San Bernardino County, and San Diego County. It had its first Headquarters at Camp Latham, west of Los Angeles this was later moved to Drum Barracks.