Trethowan (120 acres) gave name and origin to a family of small gentry. Trethowan farm house is in ruins and shows no traces of ancient work except some granite quoins. A shield over the entrance of the house which is supposed to bear the Arms of Trethowan, apparently three garbs (sheafs of grain frequently used in heraldry) has disappeared . The land is now farmed with Merthen.
The name Trethowan is still found in the Parish today (2010) Gerald Trethowan being the Chairman of the Constantine History Group and a direct descendant.
An Alan Trethouen paid the subsidy in 1327. Henry Trethowyn did homage to the Lord of Merthen for a Cornish acre held in Trethowyn in Knights service. In 1528 part of Trethowyn was held by the heirs of Trethowyn and part, with Polpry, by Gerveys of Bonallack, both under the Manor of Merthen in Knights service.
John Trethowan of Trethowan married in 1582 Avis daughter of Thomas Enys of Enys by Katherine Reskymer of Merthen. Avis Enys born and chr 15 Sept 1563 at Tremayne St Martin in Meneage. (see Vivians Visitations of Cornwall Enys family entry)
In 1649 and 1660 Thomas Trethowan was living at Trethowan which was his freehold.
In 1726 John Trethowan owned it.
After that the family appears to have sold its land to the Vyvyans of Trelowarren
n.b.There is said to be a crock of gold buried at Trethowan, and more than one vain attempt has been made to discover it!