Ruthin is a market town and community in Denbighshire, Wales, in the south of the Vale of Clwyd. It is Denbighshire's county town. The town, castle and St Peter's Square lie on a hill, skirted by villages such as Pwllglas and Rhewl. The name comes from the Welsh rhudd and din, after the colour of sandstone bedrock, from which the castle was built in 1277–1284. The Old Mill, Ruthin, is nearby.