Baron Dinevor, of Dinevor in the County of Carmarthen (usually spelt Dynevor), is a title in the Peerage of Great Britain. It was created in 1780 for William Talbot, 1st Earl Talbot, with remainder to his daughter, Lady Cecil, wife of George Rice, a member of a prominent Welsh family. On Lord Talbot's death the earldom became extinct because he left no sons to succeed to it, while the barony of Talbot also held by him was inherited by his nephew. The barony of Dynevor passed according to the special remainder to his daughter, the second holder of the title. In 1787 Lady Dynevor assumed by Royal license the surname of de Cardonnel in lieu of Rice.
Her son, the third Baron, represented Carmarthen in the House of Commons and served as Lord Lieutenant of Carmarthenshire. In 1793 he assumed by Royal license the surname of de Cardonnel, but in 1817 he resumed by Royal license the surname of Rice. He was succeeded by his son, the fourth Baron. He also sat as Member of Parliament for Carmarthen. In 1824, on inheriting the estates of the Trevor family of Glynde in Sussex, he assumed by Royal license the additional surname of Trevor.
He was succeeded by his first cousin, the fifth Baron. He was the second son of the Very Reverend the Hon. Edward Rice, second son of the second Baroness. His grandson, the seventh Baron, represented Brighton in Parliament as a Conservative and served as Lord Lieutenant of Carmarthenshire. In 1916 he assumed by Royal license for himself and his issue the surname of Rhys in lieu of Rice. His son, the eighth Baron, was a Conservative Member of Parliament for Romford and Guildford. As of 2010[update] the title is held by his grandson, the tenth Baron, who succeeded in 2008.
The Rhys family claim descent from the fifteenth century Rhys ap Thomas who had been granted extensive lands throughout west Wales as a reward for raising an army in support of Henry VII's usurpation in 1485.
The heir presumptive is the present holder's second cousin Robert David Arthur Rhys