Frederica Mildmay, Countess FitzWalter

Frederica Mildmay
Countess FitzWalter suo jure Countess of Mértola
Frederica, Countess FitzWalter (circle of Joseph Highmore, 1727)
Spouse(s)	Robert Darcy, 3rd Earl of Holderness (m. 1715–21; his death) Benjamin Mildmay, 1st Earl FitzWalter (m. 1724–51; her death)
Issue Robert Darcy, 4th Earl of Holderness Caroline Kerr, Marchioness of Lothian
Full name Frederica Susanna Mildmay (née Schomberg)
Father	Meinhardt Schomberg, 3rd Duke of Schomberg
Mother	Raugravine Karoline von der Pfalz
Born	1687 Berlin
Died	7 August 1751 (aged 63–64)
Religion	Protestant

Frederica Susanna Mildmay, (née Schomberg), Countess FitzWalter, 3rd Countess of Mértola (previously Frederica Darcy, Countess of Holderness) (Berlin, 1687 – 7 August 1751) was a British peeress.

Frederica was the eldest surviving daughter of Meinhardt Schomberg, 3rd Duke of Schomberg and his second wife, Raugravine Karoline Elisabeth von der Pfalz, a daughter of Charles I Louis, Elector Palatine. On 26 May 1715, she married the 3rd Earl of Holderness and they had two surviving children:

On the death of the countess' father in 1719, she inherited his Portuguese countship of Mértola as his eldest surviving child. Her husband died in 1721 and on 18 June 1724, she married Hon. Benjamin Mildmay, who was later created Earl FitzWalter in 1730.

Via cognatic primogeniture, she was the most senior descendant of James I of England to be Protestant, but she was passed over for Sophia of Hanover. Her cognatic heir is Anthea Theresa Lycett (born Marcia Anne Miller), Countess of Mértola, eldest daughter of Diana, Baroness Conyers and Fauconberg and Countess of Mértola.