Margaret Etienne Hannah Crewe-Milnes, Marchioness of Crewe CI JP known to her friends as Peggy,[1] (1 January 1881 – 13 March 1967), styled as Countess of Crewe from 1899 until 1911; was a Rothschild family heiress, and after the death in 1929 of her father, the former Prime Minister Archibald Primrose, 5th Earl of Rosebery, she was said to be the richest woman in England.

[4] She was one of the first female justices of the peace in London, appointed as a magistrate in 1919 after the passing of the Sex Disqualification (Removal) Act 1919.

[5] Her mother, Hannah, was the daughter of Baron Mayer de Rothschild and her father was Archibald Philip Primrose, 5th Earl of Rosebery.

She was nine years old when her mother died in 1890[7] She married Robert Offley Ashburton Crewe-Milnes, the Earl of Crewe, at Westminster Abbey on 15 April 1899.

[4][8] According to The New York Times, the wedding had "no parallel in recent history, except for the Queen's Jubilee," which they attributed to her father's political career.