Richard Le Poer Trench, 2nd Earl of Clancarty, 1st Marquess of Heusden GCB GCH PC (19 May 1767 – 24 November 1837), styled The Honourable from 1797 to 1803 and then Viscount Dunlo to 1805, was an Anglo-Irish peer, a nobleman in the Dutch nobility, and a diplomat.

Clancarty was the son of William Trench, 1st Earl of Clancarty and Anne, daughter of Charles Gardiner and his seat was Garbally Court in Ballinasloe, East County Galway where he was associated with the Great October Fair.

He sat further for County Galway from 1798 to a short time before the Act of Union, when he was replaced by "Humanity Dick" Martin.

He was credited with resolving various border disputes in Holland, Germany and Italy at the Congress of Vienna, 1814–1815, and in his role as Ambassador to the Netherlands.

For his service as ambassador to The Hague, he was awarded the hereditary title of Marquess of Heusden in the peerage of The Netherlands on 8 July 1815[3] by William I of the Netherlands, following the defeat of Napoleon in Brabant, in that same province's southern reaches.