The state electorate of Mulgoa has an approximate area of 270 km².

It is comprised of the suburbs of Abbotsbury, Cecil Hills, Cecil Park, Elizabeth Hills, Erskine Park, Glenmore Park, Horsley Park, Kemps Creek, Middleton Grange, Mount Vernon, Mulgoa, Regentville and St Clair plus parts of Austral, Badgerys Creek, Eastern Creek, Len Waters Estate, Luddenham, Orchard Hills, Wallacia and West Hoxton.

It is adjacent to the locality of Blue Mountains National Park.

It is comprised of parts of the councils of Fairfield, Liverpool and Penrith.

It is surrounded by the state electorates of Blue Mountains, Cabramatta, Camden, Liverpool, Londonderry, Mount Druitt, Penrith, Prospect and Wollondilly.

It is comprised of parts of the federal electorates of Fowler, Hume, Lindsay, Mcmahon and Werriwa.