Casthorpe is hamlet in the civil parish of Barrowby and the South Kesteven District of Lincolnshire, England.

[10] In 2002 Charles Richard Ferens of Casthorpe Lodge became High Sheriff of Lincolnshire.

The hamlet is centred to the north of the junction of Denton Lane and Casthorpe Road, and is at the foot of the Casthorpe Hills which rise to 384 feet (117 m) above sea level, and mark an eastern edge of the Vale of Belvoir.

The Old Beck, a stream which runs north from the Grantham Canal, flows through the east of Casthorpe below Casthorpe Hills, eventually reaching the River Witham at Marston as the Foston Beck.

The two-storey Casthorpe Farm House on Denton Lane is of brick, partly rendered, and dating to the early 18th century.