William Philip Molyneux, 4th Earl of Sefton, KG (14 October 1835 – 27 June 1897) was a British peer. Born Viscount Molyneux, he was the eldest son of Charles Molyneux, 3rd Earl of Sefton and his wife, Mary. He was educated at Eton College, Berks. In 1854, Molyneux became an ensign in the Grenadier Guards and inherited his father's earldom the following year. He was promoted to captain in 1857, retiring a year later, when he was appointed Lord Lieutenant of Lancashire. The family seats were : Croxteth Hall, Lancs ; Abbeystead House, Lancs ; Sefton House, Belgravia Sq., London