Newcastle West or simply Newcastle is a town in west County Limerick, Ireland. It is the largest town in the county, excluding Limerick city. It is also the county town, and sits on the River Arra which flows into the River Deel. Newcastle West is in the middle of a great bowl-shaped valley in West Limerick, known one time as the valley of the Wild Boar, apparently due to the abundance of this animal here when the area was thickly wooded. The crest of the town carries the image of a wild boar. The town is partly in the civil parish of Newcastle.

County Limerick is a western county in Ireland. It is in the province of Munster and is located in the Mid-West which comprises part of the Southern Region. It is named after the city of Limerick. Limerick City and County Council is the local council for the county. The county's population at the 2022 census was 209,536 of whom 102,287 lived in Limerick City, the county capital.