Sir William Myddelton (1694-1718), 4th Bart, of Chirk Castle, died unmarried and the baronetcy became extinct. The estate of Chirk Castle, with the lordships of the manor of Chirk, Chirkland, and Ruthin passed to Robert (d. 1733), younger son of the 1st Bart, who died without issue. He was succeeded by his brother, John (d. 1747). On the death of John's grandson, Richard Myddelton (d. 1796), the Chirk Castle estate passed to his eldest sister, Charlotte, who had married Robert Biddulph of Cotton Hall, Worcestershire, in 1801. Robert assumed the additional surname and arms of Myddelton by royal licence in 1801. Their eldest son and heir was Colonel Robert Myddelton-Biddulph (1805-1872) of Chirk Castle, Denbighshire, and Burghill, Herefordshire.
Scope and content: Deeds relating to the Chirk Castle estate in the lordships of Chirk and Ruthin, manors of Collion, Dogfeiliog, Llannerch and Ruthin, various parishes in Denbighshire, and in the counties of Merionethshire, Montgomeryshire, Essex, Gloucester, Hampshire, Leicestershire, Northamptonshire, Oxfordshire and Surrey, 1723-1832; Chancery papers relating to the division of the Chirk Castle estate among the sisters and co-heiresses of Richard Myddleton (died 1796), 1814-1819; and Myddleton family wills, 1717-1826.