Oldcastle is a town in County Meath, Ireland. It is located in the north-west of the county near the border with Cavan, approximately 13 miles (21 km) from Kells. The R154 and R195 regional roads cross in the town's market square. The town is in a townland and civil parish of the same name.

County Meath is a county in the Eastern and Midland Region of Ireland, within the province of Leinster. It is bordered by County Dublin to the southeast, Louth to the northeast, Kildare to the south, Offaly to the southwest, Westmeath to the west, Cavan to the northwest, and Monaghan to the north. To the east, Meath also borders the Irish Sea along a narrow strip between the rivers Boyne and Delvin, giving it the second shortest coastline of any county. Meath County Council is the local authority for the county.