The house and estate is the historic seat of the Boscawen family, Viscounts Falmouth. The original medieval house was ransacked in the 17th century during the English Civil War. In the new house the date 1652 is carved in stone above the side gate. It was enlarged in the early 19th century to the designs of William Wilkins, the architect of the National Gallery in London.
Tregothnan is famous for its large private botanical garden and arboretum. Tregothnan is not open to the public, but guided visits to the garden may be arranged.
In 1872 the land holdings of Viscount Falmouth, of Mereworth Castle, Maidstone, Kent, were listed in the top ten land holdings in Cornwall, with an estate of 25,910 acres (10,490 ha), 3.41% of the total area of Cornwall.