Through the course of the Civil War, the brigade was composed entirely of units from New Jersey, the only Union brigade during the war to be constituted as such. Its origins were on May 4, 1861, when New Jersey was directed by the Federal government to fill a quota of three infantry regiments to serve a three-year term of enlistment. Recruitment took place for the new regiments all over the state, and on May 21, 1861, the 1st New Jersey Volunteer Infantry was mustered into the Union Army at Camp Olden in Trenton, New Jersey, under Maj. Theodore T. S. Laidley of the United States Regular Army. The 1st New Jersey was then followed into Federal service by the 2nd New Jersey Volunteer Infantry (May 28, 1861) and the 3rd New Jersey Volunteer Infantry.