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.

Oldcastle acts as a retail and service centre for the surrounding hinterland, and is also home to a number of furniture-manufacturing and engineering businesses.

The town's bed-manufacturing industries have included firms such as Gleneagle Woodcrafts, Briody Bedding and Respa Bedding which are a major source of employment for the area. In 1999, a fire broke out at Gleneagle Woodcrafts, killing one woman. The site has since been restored and continues to operate. A similar event occurred on the night of October 31, 2020, when a fire tore through an Oldcastle Co-Operative building.

There are the engineering firms located in the parish of Moylagh, County Meath, approximately 5.0 mi (8 kilometres) from the town. These industries have attracted immigrants to the area for work, including from Lithuania and Poland. As of the 2016 census, for example, there were approximately 210 Lithuanian-born people living in the town.

Oldcastle is located a short distance from the Loughcrew Cairns, a tourist attraction that was built around 3300 BCE as passage tombs.