The State Archives in Osijek (SAO) conducts the organised protection of archival materials and supervision of in the field emerging archival materials in the area of Osijek-Baranja County. It consists of eight departments, has a reading room with eight seats, a small lecture hall with 30 seats, and the storage space full of archival materials. Today, the SAO holds more than 7,300 linear meters of archival records, arranged into more than 1,720 archival funds and collections. The earliest preserved archival record dates from the end of the 17^th century. The documents written before 1848 are mostly in Latin, which was the official language, but there is a considerable amount of material in German, written in the cursive Gothic style. Since 1848, the records were mostly written in Croatian, less in German, and very little in Hungarian and Serbian (Cyrillic).
After World War II, a new approach to dealing with archival records as cultural heritage was adopted. An archival storage facility (sub-station) of the State Archives Office in Zagreb was established in Osijek in 1947. From then on, we can speak of the systematic and organised protection and supervision of archival records in this institution. In 1956, the Archives became an independent organisation – the Archives in Osijek. In 1957, the Communist Party Archives were established as a part of the Archives. It collected, processed and published historical sources regarding the history of the Workers' Movement, the Communist Party and the Partisan struggle during World War II. This archive was integrated into the then Historical Archives of Osijek in 1962.
Until 1971, the Archives were located in Kuhačeva street no. 27. Due to the increasing need for archival storage, the Archives were moved (1972-1975) to the present location in Kamila Firingera street no. 1. The building has 2,000 square meters of space, broken down into 1,500 square meters of storage space, a workshop of 100 square meters, with the rest divided among offices and workrooms. The Archives Building was severely damaged in the Homeland War in 1991/1992. It was entirely reconstructed in 1996. It is a first-class cultural monument in the Osijek fortress, and it is protected as an urban heritage site.
In 1993, all of the regional archives (including the SAO), had to change their names into the Historical Archives. The newest name change came in April 1998, and since then the Archives carry the current name: State Archives in Osijek. Its territorial jurisdiction included the areas of three counties - Osijek-Baranja, Vukovar-Srijem and Virovitica-Podravina - but since 1 May 2009, it has been limited to Osijek-Baranja County.