The suburb is on the traditional lands of the Dharawal and Gundungurra people. Mount Annan is the name given to a high point in the western part of the locality and is 190 metres above sea level. It only appears on published maps after 1834. This point was part of Glenlee which was owned by William Howe, who built a fine Georgian house (1824) on the property. Glenlee was acquired by James Fitzpatrick in the 1850s and his descendants ran it as a dairy farm until 1978 with associated cropping and grazing.
The first land release for housing at Mount Annan was in late 1980s for first home buyers and low income families. Later land releases such as Garden Gates were aimed at second and third home buyers. The population growth encouraged the establishment of new shopping facilities, a leisure centre and schools.
The Mount Annan Botanic Garden is the highlight of the suburb. It is a native plant botanic garden and arboretum in an attractive garden and parkland setting and is managed by the Royal Botanic Gardens and Domain Trust.
On the eastern side of the Mount Annan Botanic Gardens is a little piece of history which was constructed in 1880. It is a water canal (aqueduct) which is partly made of sandstone blocks thought to be quarried from Mount Annan. It is part of the Upper Nepean Scheme which supplies water by gravity from the dams on upper Nepean River to Prospect Reservoir along a course of 62 km. Until Warragamba Dam was finished in 1960 this canal supplied most of Sydney’s water.
In 2001 Mount Annan had a population of 6,761, and which was an 85 per cent increase from 1996. The demographic profile of Mount Annan is predominantly young families, with 35 per cent of the population under 18 years of age.