Katherine FitzGerald, Viscountess Grandison

Katherine FitzGerald, suo jure Viscountess Grandison, was born in August 1660 at Dromana House, Villierstown, County Waterford, Ireland. She was the only child of Sir John FitzGerald of Dromana and Katherine Power. Her father died in 1664, and she inherited the Dromana estate at the age of three. Her mother died shortly after her birth, and her guardianship was held by King Charles II of England and her maternal uncle, Richard Le Poer, 6th Baron Le Poer of Curraghmore, later the 1st Earl of Tyrone.

The FitzGerald family, lords of the Decies, had retained their lands through the Cromwellian settlements, largely owing to their Protestant faith and advantageous marriage alliances, including the marriage of Katherine's aunt, Lettice, to Parliamentarian Major Richard Franklyn.

In 1673, Katherine was married to John Le Poer, the son and heir of her uncle, by Archbishop Gilbert Sheldon at Lambeth Palace. She was nearly 13 years old, and John was eight. In the same year, her uncle was elevated to the titles of 1st Earl of Tyrone and Viscount Decies. However, Katherine soon sought an annulment of this marriage, claiming her consent was not free; this occurred in 1677.

Following her attempt to annul the marriage, Katherine eloped with Brigadier-General Edward Villiers, the son of George Villiers, 4th Viscount Grandison, and Mary Leigh. Her clandestine marriage was challenged legally but ultimately declared valid, with support from her husband's influential cousin, Barbara Villiers, the mistress of King Charles II. The annulment of her previous marriage to John Le Poer resulted in her returning possession of her lands and her father's titles.

Katherine and Edward Villiers had four children: Mary Villiers, Harriet Villiers, John FitzGerald Villiers, and William Villiers. Her son, John, became the 5th Viscount Grandison and Earl Grandison and married Frances Cary. William Villiers died in 1693.

Her husband, Edward Villiers, died in 1693. Subsequently, Katherine married her third husband, General William Steuart, who served as Commander-in-Chief of Queen Anne's forces in Ireland and was a Member of the Irish Parliament for County Waterford. This marriage was childless.

On 6 January 1700, Katherine was granted the rank of Viscountess by Royal Warrant from King William III of England. She remained a prominent figure until her death in London on 26 December 1725, at the age of 65. Her death was recorded as occurring while she was insane. She was buried in Westminster Abbey. After her death, her third husband, William Steuart, married Eliza Alston, daughter of Sir Rowland Alston, a baronet, in 1725.