Coordinates: 50°05′37″N 5°10′45″W / 50.0937°N 5.1791°W
Merthen Manor (Cornish: Merdhin, meaning sea fort) is a 16th-century manor house in west Cornwall, England, UK. For the majority of its usage it has been in the ownership of the prominent Cornish family, the Vyvyan family. The house is set in over 100 acres (40 ha) of woodland which, along with the shoreline of the Helford River, is designated as Merthen Woods Site of Special Scientific Interest (SSSI).
The land of Merthen was originally part of the manor of Winnianton, which was given to Richard, 1st Earl of Cornwall by his brother, Henry III, in 1225, who then swapped it with Gervase de Tintagel for Tintagel Castle. Ralph Reskymer obtained Merthen in the early part of the 15th century, and it became family seat of the Reskymers.
The current manor house is thought to have been built in 1575 by John Reskymer and his wife Grace, due to their coat of arms over the entrance, although it may originate earlier and the coat of arms are an indication a remodelling or reduction. Grace died in 1627, 10 years after her husband, and in 1629 it was sold to Sir Francis Vyvyan of Trelowarren and has remained with the family since.