Official Records of the Union and Confederate Armies in the War of the Rebellion (from Cornell University Library)

DOC. W 45.5:volumes 1-128, Floor 4 documents stacks

The 128 volumes of the Official Records, also referred to as OR, provide the most comprehensive, authoritative, and voluminous reference on Civil War operations. The reports contained in the Official Records are those of the principal leaders who fought the battles and then wrote their assessments days, weeks, and sometimes months later. The Index for the series is located at the Reference Desk on Floor 2.

See also, A User's Guide to the Official Records of the American Civil War located on Floor 3, E464 .A351993.

Citing the Official Records example: 

U.S. War Department, War of the Rebellion: A Compilation of the Official Records of the Union and Confederate Armies, 128 vols. (Washington: Government Printing Office, 1880-1901), ser. 1, vol. 32, pt. 1, 608-17.

Supplement to the Official Records

DOC. W 45.5:1994 volumes 1-100, Floor 4 documents stacks

Supplement includes reports not previously included within the original publication of Official Records of the Union and Confederate Armies in the War of the Rebellion.

Official Records of the Union and Confederate Navies in the War of the Rebellion

 DOC. N 16.6:volumes 1-30, Floor 4 documents stacks

These are the records of the Naval War Records Office during the Civil War, which are strong on Confederate diplomatic correspondence. The ORN, as this set is commonly called, is a valuable source of naval affairs during the war. In addition to day-to-day naval operations, the set contains large amounts of diplomatic correspondence. The ORN should be used in conjunction with its companion set, the ORA, the official records of the Union and Confederate armies.

Report of the Adjutant General of the State of Illinois (from Open Library)

E 505.2 I3, Floor 3

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.

Civil War Naval Chronology, 1861–1865. Washington, DC: Government Printing Office, 1971.

DOC. D 207.2:C 49/COMP., Floor 4 Documents Stacks