South Dublin is an administrative county formed from part of the traditional county of Dublin. The centre of Local Government of South Dublin is Tallaght. South Dublin achieved county status in the 1993 Local Government (Dublin) Act, and more formally in the 2001 Local Government Act. It was created alongside two other authorities to replace Dublin County Council.

The Coat of Arms for South Dublin reads "This We Hold In Trust" in both English and Irish, while incorporating elements of the history, geography and present day infrastructure of the area.

South Dublin is the last county in Ireland to have any alterations made to its boundary, these being made in 1993 to accommodate the M50 motorway. It is also the last county to undergo a name change, its original name of "Belgard" (An Bealach Ard) being changed to South Dublin when the area was altered from being an Electoral County to an Administrative County in 1994 (Fingal and Dun Laoghaire-Rathdown's boundaries and names were both set in 1985). The name of Belgard did have a historical association with the area, being the designation of one of the border fortresses of the Pale which existed in that area. It was altered however under the view that the name Belgard would create associations to certain areas of modern development in Tallaght that now also use that name. The county is still identified as Belgard by certain Government departments to differentiate it from the geographical area of south Dublin. Representations can be made at any time by the elected members of the County Council to the Government requesting a legal name change.

The area of South Dublin covers 222.74 square kilometres and lies 15 km south west of the capital. It is bounded by the Dublin Mountains to the south and stretches from the River Liffey at Lucan through Palmerstown, Clondalkin, south to Newcastle, Rathcoole, Saggart. It includes Tallaght West, South and Central and stretches east to Templeogue and Rathfarnham. South Dublin is bordered by the Counties of Kildare, Wicklow, Fingal and Dun Laoghaire-Rathdown, as well as Dublin City. The Institute of Technology, Tallaght is located within the county. The county is considered part of the "Greater Dublin Area".