Thornhill (Welsh: Draenen Pen-y-graig; meaning draen thorn + -en one + pen top + 'y' the + craig rock [mutated to 'graig']) is a community in the north of the city of Cardiff, Wales.

Thornhill also houses a few tucked away historical sites including the remains of a castle situated close to the Caerphilly/Thornhill border known as Castell Morgraig.

The 27 and 28 service runs through Thornhill and terminates at the Central Bus Station at regular intervals.

Stagecoach service 25 follows a route along Thornhill road on its way to the University Hospital of Wales and Cardiff City Centre.

Stagecoach Wales have operated the 86 service since 1 April 2019 after Cardiff Bus withdrew from the route.