Pentillie Castle is a grade II* listed country house and estate on the bank of the River Tamar in Paynters Cross, near to St Mellion, in Cornwall, England, in the United Kingdom. The secular parts of the nearby village of St Dominick once belonged to the estate.

The Tamar is a river in south west England that forms most of the border between Devon and Cornwall. A part of the Tamar Valley is a World Heritage Site due to its historic mining activities.