The state electorate of Heysen has an approximate area of 1,100 km².

It is comprised of 41 suburbs including Aldgate, Ashbourne, Biggs Flat, Blackfellows Creek, Bradbury, Bridgewater, Bugle Ranges, Bull Creek, Chapel Hill, Crafers West, Dorset Vale, Echunga, Flaxley, Gemmells, Green Hills Range, Hahndorf, Heathfield, Highland Valley, Ironbank, Jupiter Creek, Kangarilla, Kuitpo Colony, Longwood, Mcharg Creek and Meadows plus parts of another 12 suburbs.

It is comprised of the locality of Kondoparinga plus parts of Belvidere, Bremer, Finniss, Kuitpo, Macclesfield, Nangkita, Noarlunga, Onkaparinga and Strathalbyn.

It is comprised of parts of the councils of Adelaide Hills, Alexandrina, Mount Barker District and Onkaparinga City.

It is surrounded by the state electorates of Bragg, Davenport, Finniss, Fisher, Hammond, Kavel, Mawson and Waite.

It is within the federal electorate of Mayo.