He was the elder son of Henry Willett of St Kitts, who married c. 1718, Elizabeth, eldest daughter of Colonel John Stanley of Nevis.
[3] In London, Willett had a town house in Dean Street, Soho, and in 1751 he bought the estate of Merley, a manor of Canford Magna, Dorset.
A printed account of this room and a view of the house are in John Hutchins's Dorset (2nd edit.
12); views and plans are also in Woolfe and Gandon's continuation of Campbell's Vitruvius Britannicus.
A description of the library was printed in octavo, in French and English, in 1776; it was reprinted by John Nichols, with illustrations of the designs, in 1785.
He had been a patron of Georg Dionysius Ehret who spent the summers of many years at Merley House, its library containing "a copious collection of exotics" by him.
His first wife, Annabella Robinson, died on 10 December 1779, aged 60; a tablet to her memory and that of her husband was placed on the south side of the chancel of Canford Magna church.
She died at Dean Street on 11 May 1815, aged 69, and was buried in the south cloister of Westminster Abbey.
Henry Ralph Willett, a descendant of John Willett Adye, who died in The Albany, London, in December 1857, collected coins and pictures, including twenty-six paintings and sketches by Hogarth.