Castlemaine (/ˈkæsəlmeɪn/) is a small city in Victoria, Australia, in the goldfields region of Victoria about 120 kilometres northwest by road from Melbourne and about 40 kilometres from the major provincial centre of Bendigo. It is the administrative and economic centre of the Shire of Mount Alexander. The population at the 2011 Census was 6,751.
It was named by the chief goldfield commissioner, Captain W. Wright, in honour of his Irish uncle, Viscount Castlemaine.
Castlemaine began as a gold rush boomtown in 1851 and developed into a major regional centre, being officially proclaimed a City on 4 December 1965, although since declining in population.
It is home to many cultural institutions including the Theatre Royal, the oldest continuously operating theatre in mainland Australia.