Fonds GB 0210 MOSBRA - Bryngwyn (Montgomeryshire) Estate Records,

Little is known of the Mostyn family of Bryngwyn until a William Mostyn of Bryngwyn whose will was proved in 1729. John Mostyn, esq., was living at Bryngwyn in 1740 with his brothers William Mostyn and Humphrey Mostyn, esqs, when William married Grace, daughter of Robert Wynne of Plas Newydd, Denbighshire, esq. The capital messuage of Plas Kynaston in the parish of Ruabon, Denbighshire, was included in the marriage settlement.

William Mostyn (d. c.1786) is described as of Bryngwyn, esq., 1755-1769, and of Plas Kynaston, esq., 1783-1787. His eldest son and heir apparent was William Mostyn (fl. 1769-92, d. pre-1812) the younger, of Bryngwyn, esq. He married Rebecca (fl. 1769-92) daughter of Rebecca Dod of Edge, Cheshire, widow, in 1769. He had assumed the surname Owen by 1774, and was known as William Owen of Woodhouse, esq., formerly William Mostyn the younger. Their eldest son and heir apparent was also called William Owen (fl. 1791-1813) of Woodhouse, esq.

Bryngwyn was mortgaged in 1787 to William Jennens of Grosvenor Square, London, and Plas Kynaston was mortgaged in 1788 by William Owen to John Freer of Birmingham, surgeon. In 1791 William Owen, his wife and son put Bryngwyn into the hands of trustees, members of the Wynne family of Plas Newydd and the Dod family of Edge. Jenners was still receiving interest payments in 1798, as was Freer in 1797.