 He died at 13 Brooksby Street, South Islington, London, on 21 February 1845.In 1800 Illingworth published an "Inquiry into the Laws, Antient and Modern, respecting Forestalling, Regrating, and Ingrossing".He transcribed and collated the "Statutes of the Realm" from Magna Carta to nearly the end of the reign of Henry VIII; transcribed and printed the "Quo Warranto Pleadings" (Record Commission, 1818) and the "Hundred Rolls" (Record Commission, 1812–18), and wrote the preface and compiled in Latin the subject index to the "Abbreviatio Placitorum" (Record Commission, 1811).