Jacob Pleydell-Bouverie, 4th Earl of Radnor (18 September 1815 – 11 March 1889) was a British nobleman and army officer. He was the son of William Pleydell-Bouverie, 3rd Earl of Radnor and Judith Anne St John-Mildmay. He was styled Viscount Folkestone from 1828 until 1869. Folkestone was educated at Harrow and Christ Church, Oxford. On 2 October 1837, he was commissioned a cornet in the Salisbury Troop of the Royal Wiltshire Regiment of Yeomanry. He was a lieutenant in the Regiment from 20 May 1840 to April 1847. They had twelve children: