Cassandra Willoughby, Duchess of Chandos

Cassandra Willoughby, Duchess of Chandos (23 April 1670 – 16 July 1735) was an English historian, travel writer and artist.

She was the daughter of Francis Willoughby of Wollaton, Nottinghamshire, a Fellow of the Royal Society, and a writer on natural history, and his wife Emma, the daughter of Sir Henry Barnard of Bridgnorth, Shropshire and London.

When her 19-year-old brother Francis disagreed with his stepfather's handling of his finances, Cassandra accompanied him in 1687 to the Willoughby family's earlier seat, Wollaton Hall in Nottinghamshire: "This proposall [of her brother's] I was much delighted with, thinking it would be no small pleasure for me to be Mrs of Wollaton, and to doe whatever I had a mind to." She then oversaw restoration of the gardens and rebuilding of the house over a quarter of a century.

In 1713, at the age of 43, Cassandra married her wealthy cousin, James Brydges FRS, at Chelsea College Chapel. She was his second wife. Brydges' social standing rose the following year when he was made Earl of Carnarvon and inherited a barony and baronetcy when his father, the 8th Baron Chandos of Sudeley, died; in 1719 he became Duke of Chandos, and Cassandra the Duchess.

Kneller's 1713 portrait of the Chandos family is believed to show Cassandra rather than the Duke's first wife who was the mother of the two children in the picture.

The National Gallery of Canada has a portrait of Cassandra and her husband by Sir Godfrey Kneller dated 1713 which also features Brydges' two sons by his first wife.

Cassandra died childless aged 65, and was buried at St Lawrence, Whitchurch near the ducal seat Cannons.

Both the mother and sister of Jane Austen were named after Cassandra, to celebrate their link with a ducal family; Jane's mother was the granddaughter of the first Cassandra's sister-in-law, Mary Brydges.

Before she married she compiled a history of her father's family she titled The Continuation of the History of the Willoughby Family which is preserved in the Manuscripts Department at Nottingham University Library. Some of her correspondence from before and after her marriage has been preserved at the Shakespeare Birthplace Trust Record Office, at the North London Collegiate Schooland the Huntington Library and Art Gallery, in San Marino, California. In addition, there are travel writings and genealogies.