William Pleydell-Bouverie, 9th Earl of Radnor (born 5 January 1955), of Longford Castle, Wiltshire, is an English peer and landowner.
The son of Jacob Pleydell-Bouverie, 8th Earl of Radnor, by his marriage to Anne Garden Seth-Smith, daughter of Donald Farquharson Seth-Smith, Pleydell-Bouverie was educated at Harrow and the Royal Agricultural College, Cirencester. Until the death of his father, he was known by the courtesy title of Viscount Folkestone.
In 1996 he married Melissa Stanford, daughter of J. K. E. Stanford,formerly Director-General of the Leonard Cheshire Foundation, and a grand-daughter of the author J. K. Stanford. They have four sons and two daughters: Lady Hope (born 1997); Jacob, Viscount Folkestone (born 1999); Luke (born 2000); Dan (born 2002); Edward (born 2004); and a daughter born in 2007. The heir apparent is their eldest son, Jacob Pleydell-Bouverie, Viscount Folkestone.
In 2014, Radnor declined to meet a distant relation, the Dutch architect Jan des Bouvrie, who had found that his ancestor Jehan de le Bouvrie (born about 1480), was also the ancestor of the Earls of Radnor.
In 2015, he declined to be interviewed by the Salisbury Journal about plans to build houses on fields he owned near Salisbury Cathedral, but a statement was issued by his estate office.
The Daily Express reported in May 2016, during the European Union referendum campaign, that in 2014 Radnor's company Longford Farms Limited received £453,618 from the European Union to pay for the upkeep of the Longford Castle estate.