Newcastle is a village in the south-western part of South Dublin county, Ireland. It is also a civil parish in the barony of the same name. It was the location of the castle of the barony, which in historical and official documents is described as Newcastle-Lyons. The area is still primarily rural in nature. Newcastle village is within the administrative area of …Newcastle is a village in the south-western part of South Dublin county, Ireland. It is also a civil parish in the barony of the same name. It was the location of the castle of the barony, which in historical and official documents is described as Newcastle-Lyons. The area is still primarily rural in nature. Newcastle village is within the administrative area of South Dublin County Council.