The phrase Tre, Pol and Pen is used to describe people from or places in Cornwall

Cornwall

Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...

, UK. The full rhyming couplet runs: By Tre, Pol and Pen shall ye know all Cornishmen.

Many Cornish

Cornish people

The Cornish are a people associated with Cornwall, a county and Duchy in the south-west of the United Kingdom that is seen in some respects as distinct from England, having more in common with the other Celtic parts of the United Kingdom such as Wales, as well as with other Celtic nations in Europe...

 surnames and place names still retain these words as prefixes, such as the name Trelawny and the town of Polperro

Polperro

Polperro is a village and fishing harbour on the south-east Cornwall coast in South West England, UK, within the civil parish of Lansallos. Situated on the River Pol, 4 miles west of the neighbouring town of Looe and west of the major city and naval port of Plymouth, it is well-known for...

. Tre in the Cornish language

Cornish language

Cornish is a Brythonic Celtic language and a recognised minority language of the United Kingdom. Along with Welsh and Breton, it is directly descended from the ancient British language spoken throughout much of Britain before the English language came to dominate...

 means a settlement or homestead; Pol, a pond, lake or well; and Pen, a hill or headland.

Examples in Cornish surnames

• Richard Trevithick
  Richard Trevithick
  Richard Trevithick was a British inventor and mining engineer from Cornwall. His most significant success was the high pressure steam engine and he also built the first full-scale working railway steam locomotive...
  
  
• Sir Jonathan Trelawny, 3rd Baronet
• David Penhaligon
  David Penhaligon
  David Charles Penhaligon was a British politician from Cornwall who was a Liberal Member of Parliament from October 1974 until his death...
  
  
• Edward William Wynne Pendarves
  Edward William Wynne Pendarves
  Edward William Wynne Pendarves was Member of Parliament for West Cornwall from the creation of the Constituency on 19 December 1832 until the year of his death....