Jacob Pleydell-Bouverie, 4th Earl of Radnor (18 September 1815 – 11 March 1889), 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.
He married Lady Mary Augusta Frederica Grimston, daughter of James Walter Grimston, 1st Earl of Verulam, on 3 October 1840. They had twelve children:
Folkestone was appointed High Sheriff of Wiltshire in 1846 and a deputy lieutenant of Berkshire on 2 May 1855. He succeeded his father as Earl of Radnor in 1869 and was appointed Lord Lieutenant of Wiltshire in 1878.
Radnor served as Governor of the French Hospital. Successive Earls of Radnor were governors of the hospital from the eighteenth century to 2015.