Oldcastle (Irish: tSeanchaisleán) is a town in County Meath, Ireland. It is located in the north-west of the county near the border with Cavan, approximately 100 km from Dublin. The R154 and R195 regional roads cross in the town's market square. As of the 2006 census the town's population stood at 2,226.
In recent years Oldcastle has grown, being an important destination for workers from Eastern Europe who come to work in the numerous industries, particularly furniture, bedding and victualling located in the area.
Oldcastle (Tecumseh) twinned with Oldcastle Co. Meath in 1999. There have been many visits made over the past ten years. An official twinning declaration was signed at the 10th anniversary celebration in 2009 and is displayed in both town halls.