 The eldest son of Jerome William Knapp, Esq., of Chieveley, Berkshire, by his wife, Sarah Preston (heiress of her brother, Alderman Sir Thomas Preston), Knapp married, in 1758, Sarah daughter and eventual heiress of George Noyes, of Southcote, Berkshire previously of Andover, Hampshire (and descendant of William Noyes) by his wife, Anne, heiress of William Noake, High Sheriff of Berkshire.He and his wife had eleven children, among whom were Jerome William Knapp, DCL, Thomas George Knapp, solicitor (for whom he secured founder's kinship at St John's College, Oxford), and Mary Anne, who married The Hon William Best MP (later 2nd Baron Wynford).His family divided its time between London, and Symeon's Court (now Oxfordshire).