Granville Penn was the brother of John Penn [1760-1834], governor of the Isle of Portland. John Penn had Pennsylvania castle built on the island, and after his death the castle and its contents were inherited by Granville. Granville was also the principle heir of Philadelphia Hannah Freame [1740/1741-1826], granddaughter of William Penn [1644-1718], the founder of Pennsylvania. In 1770 Philadelphia had married the widowed Thomas Dawson [1725-1813], who in that same year was elevated to the Irish peerage, as Baron Dartry of Dawson's Grove. Dawson was the son of Dublin banker Richard Dawson and his wife Elizabeth Vesey Dawson. From 1749-1768 Thomas Dawson served an a member of Parliament for County Managhan [Ireland]. He was married firstly in 1754 to Lady Anne Fremor, daughter of the first Earl of Pomfret, with whom he had a son and a daughter. Dawson and his second wife had a son and daughter as well. In 1795 he was made Viscount Cremorne, and in 1797 he became Baron Cremorne of Castle Dawson. Dawson was a patron of the arts and a collector of paintings. Gilbert Stuart painted his portrait, as well as that of the Viscountess, and he was included on Stuarts' 1895 list of those patrons who were to receive copies of the artist's portrait of George Washington (although it is unknown whether he actually received one). Viscount Cremorne displayed his collection, which also included works by American artists Copley and West, at his London residence along the Thames, Cremorne House. [Compiled from sources and references recorded on CMS]
Wainwright, Nicholas B. "The Penn Collection." Pennsylvania Magazine of History and Biography 87, no. 4 (October 1963):393-419
Genealogies of Pennsylvania Families from the Pennsylvania Genealogical Magazine. 3 vols. Baltimore, 1982: 2:568-569, 625-626.