There remain gaps in our understanding of mosquito-borne arboviruses, their emergence, and public health importance in Australia. Annual mosquito and arbovirus surveillance has been undertaken in New South Wales (NSW) since the late 1970s to monitor for the human pathogens, Ross River (RRV), Barmah Forest (BFV), Murray Valley Encephalitis (MVEV), and West Nile/Kunjin (WNV_KUN) viruses. During this period, viral isolates from cell culture that could not be identified by Fixed-Cell Enzyme-linked immunosorbent assay FC-ELISA were collected and retrospectively identified by molecular methods. Ninety-nine isolates from 12 mosquito species captured in 20 locations were identified as members of the families Bunyaviridae: Trubanaman virus (TRUV) (N = 7) and Gan Gan (GGV) (N= 11); Reoviridae: Wallal virus (WALV) (N = 5), Warrego virus (WARV) (N = 7) and Stretch Lagoon orbivirus (SLOV) (N = 39); Rhabdoviridae: North Creek virus (NORCV) (N = 2), Beaumont virus (BEAUV) (N = 20) and Togaviridae: Whataroa virus (WHAV) (N = 8). The majority (N = 81) of viruses were from the inland locations of NSW, whereas GGV and NORCV were found only along the coastal regions. GGV and TRUV are recognised human pathogens whereas SLOV, WALV and WARV are associated with disease in livestock and marsupials. These viruses are not part of the routine surveillance panel and in favourable environmental conditions, the emergence of these may present a human and agricultural health challenge. This study is the first, that we know of, to report the spatiotemporal occurrence of these arboviruses in NSW over almost three decades.