South Dublin (Irish: Áth Cliath Theas) is a county in Ireland. It is part of the Dublin Region and is also located in the province of Leinster. It is named after the city of Dublin. South Dublin County Council is the local authority for the county. The population of the county is 246,935 according to the 2006 census.

The county seat is Tallaght. Other important centres of population are Lucan and Clondalkin. Much of the county is heavily urbanised but small rural settlements exist in the western parts of the county. South Dublin has a population of 246,935 according to the 2006 census. The heraldic crest for South Dublin reads "This We Hold In Trust" in both English and Irish, while incorporating elements relating to the history, geography and present day infrastructure of the area.

South Dublin has an area of 222.74 square kilometres. It is bounded by Dublin city (15 km to the north east), the Dublin mountains and County Wicklow to the south, the River Liffey to the north separating it from Fingal, and County Kildare to the west

Dublin ( /ˈdʌblɨn/; locally /ˈdʊbᵊlən/; Irish: Baile Átha Cliath, meaning "town of the hurdled ford", pronounced [blʲaˈklʲiə] or Áth Cliath, [aː klʲiə], occasionally Duibhlinn) is the capital and most populous city of Ireland. The English name for the city is derived from the Irish name Dubhlinn, meaning "black pool". Dublin is situated near the midpoint of Ireland's east coast, at the mouth of the River Liffey and the centre of the Dublin Region.

Originally founded as a Viking settlement, it evolved into the Kingdom of Dublin and became the island's principal city following the Norman invasion. The city expanded rapidly from the 17th century; it was briefly the second largest city in the British Empire and the fifth largest in Europe. Dublin entered a period of stagnation following the Act of Union of 1800, but it remained the economic centre for most of the island. Following the partition of Ireland in 1922, the new parliament, the Oireachtas, was located in Leinster House. Dublin became the capital of the Irish Free State and later the Republic of Ireland.