The histories of Illinois Civil War regiments and units are included in the first eight volumes of the nine volume publication, Report of the Adjutant General of the State of Illinois (1900-1902). (The ninth volume lists units of the Black Hawk, Mexican and Spanish-American Wars as well as the War of 1812.) The histories, some written shortly after the war's end, are the work of numerous authors throughout the intervening years. The 1886 version of the Adjutant General's Report included regimental histories compiled by that office which had not previously been published.
The final 1900-1902 republication of the report incorporated revisions and corrections to the histories. In recognition of the service of Illinois' six regiments during the Mexican War, the assignment of regimental numbers for infantry began with seven.