Formal Name: Commonwealth of Australia. Short Form: Australia. Term for Citizen(s): Australian(s). Capital: Canberra. Major Cities: In order of size, the largest cities in Australia are Sydney (4.2 million), Melbourne (3.6 million), Brisbane (1.7 million), Perth (1.4 million), and Canberra (323, 000). Independence: The British colonies of Australia were federated and the Commonwealth of Australia established on January 1, 1901.