His seats in Devon were Powderham Castle, which he greatly remodelled, and Forde House, Wolborough, near Newton Abbot. His townhouse in Exeter was the site of the present Devon and Exeter Institution at 7 Cathedral Close, on the north side of the Cathedral Green. It was at one time, like Forde, home of the Parliamentary general, Sir William Waller, whose daughter Margaret Waller was the wife of Courtenay's great-grandfather Sir William Courtenay, 1st Baronet (d.1702). Parts of Waller's building survive at the rear and the gatehouse range fronting the Close. The old hall and kitchen were demolished in 1813 to make way for the Institution and in their place and on the former courtyard are now situated the libraries.[3]
Overmantel in Exeter townhouse
Overmantel circa 1750, in former townhouse of Courtenays of Powderham, now home of the Devon and Exeter Institution, 7 Cathedral Close, Exeter. The left-hand painted panel shows the arms of William Courtenay, 1st Viscount Courtenay (1711-1762) impaling the arms of Finch, the family of his wife. The sinister supporter is one of the Finch heraldic griffins, the dexter one is the Courtenay boar. The Courtenay motto is shown underneath: Ubi lapsus quid feci ("Where did I slip what have I done"). The panel on the right shows the arms of Bishop Peter Courtenay (1432–1492), Bishop of Exeter and Winchester, of the Powderham family. His arms (Courtenay with each point of the label charged with three plates for difference) are impaled by the arms of the See of Winchester. The whole is circumscribed by the Garter. The supporters are: dexter, the Courtenay dolphin, sinister, the Courtenay boar. The motto beneath is: Quod verum tutum ("What is true is safe").