Military Organization and Rank during the Civil War – Encyclopedia Virginia
regiment – ten companies, commanded by a colonel brigade – four to six regiments, commanded by a brigadier general division – three to four brigades, commanded by a brigadier general or major general corps – several divisions, commanded by a major general army – several corps, commanded by a major general or lieutenant general department – the bureaucratic overseer of armies in the field; Union departments were often, but not always, named for rivers, Confederate departments for states or regions. Regiments were generally numbered and named for the state in which they were organiz...
Source: encyclopediavirginia.org
