South Dublin South Dublin South Dublin () is a county in Ireland, within the province of Leinster, and the Dublin Region, a successor to County Dublin, from which its name derives. South Dublin County Council is the local authority for the county. The county contains both dense suburbs of Dublin and stretches of unpopulated mountain. In 2011 it had a population of 278,749, making it the third most populous county in the state. South Dublin has an area of 222.74 square kilometres. It is bounded by Dublin City (15 km to the north east), the River Liffey (separating it from Fingal to
Newcastle (County Dublin barony) Newcastle (County Dublin barony) Newcastle () is a feudal title of nobility and one of the baronies of Ireland. It was constituted as part of the old county of Dublin. Today, it lies in the modern county of South Dublin. At the heart of the barony is the civil parish of the same name - Newcastle - which is one of eleven civil parishes in the barony. The ruins of the eponymous castle, also known as Newcastle-Lyons, are located in the townland of Newcastle South. The town with the biggest population in the barony is Lucan. It is one of