Thirlwall Castle is a 12th-century castle in Northumberland, England, on the bank of the River Tipalt close to the village of Greenhead and approximately west of Hexham. It was built in the 12th century, and later strengthened using stones from nearby Hadrian's Wall, but began to fall into disrepair in the 17th century. The site is protected by Grade I listed building and Scheduled Ancient Monument status.