It was located in the western suburbs of Sydney, and included the suburbs of Fairfield, Smithfield, Kemps Creek, St Clair, Horsley Park and those parts of the suburb of Prospect south of the Great Western Highway which were the least populous parts of the suburb.

The Prospect Reservoir was located within the Division, from which it took it's name.

The origins of the Division date back to the redistribution of 21 November 1968, and was first contested at the 1969 Federal election.

Following the 2009 redistribution of New South Wales, the division was renamed McMahon to honour former Prime Minister Sir William McMahon.

[1] McMahon was first contested at the 2010 federal election.