 In the case of "Roe v Brenton", Illingworth produced from the Lord Treasurer's Remembrancer's office an extent of the assessionable manors of the Duchy of Cornwall in the reign of Edward II; and in the case of the Mayor and Corporation of Bristol against Bush he brought forward rolls of the reign of Henry VI, which established the rights of the Corporation of Bristol to all the tolls on shipping coming in and out of the port.He gave evidence to the second committee of the House of Commons regarding the record commissioners on 2 March 1836.Before his death Illingworth became blind and fell into poverty; and a subscription was made for him by the Incorporated Law Society.