The William Street frontage features a random patterned wall at the main entrance under a low-pitched copper-sheathed roof. The western wall is decorated with Lindsay Edward's large glass mosaic mural, , the design suggesting "primitive organic forms indicative of growth and development". On the river side is Leonard Shillam's aluminium sculpture approximately high. Entitled "Enlightenment", it depicts three figures reaching towards the sun, symbolising the dissemination of enlightenment to mankind. To the south the extension was designed as a series of concrete fin walls providing views of the river, private work areas and shade from the sun. The Old State Library Building was listed on the Queensland Heritage Register on 21 October 1992 having satisfied the following criteria. The place is important in demonstrating the evolution or pattern of Queensland's history. The former State Library provides evidence of the importance of the Queensland Museum as an institution in late nineteenth century Brisbane scientific and cultural life. The former State Library is significant for its historical association with the 1958–59 extension, the major centennial project by the Queensland Government and for its association with the State Library of Queensland since 1902. The place demonstrates rare, uncommon or endangered aspects of Queensland's cultural heritage. The building is significant as an example of an 1870s public building in central Brisbane. The place is important because of its aesthetic significance. The building is an integral member of the most prominent, important and cohesive group of government buildings in Queensland. As a fine classical facade by FDG Stanley, the building is significant for its architectural quality.