Alleyne FitzHerbert, 1st Baron St Helens, PC (1 March 1753 – 19 February 1839) was a British diplomat.
He was Minister Plenipotentiary to Russia from 1783 to 1788, appointed Chief Secretary for Ireland and a member of the Privy Council (Great Britain & Ireland) in 1787, serving in the former position until 1789.
He was Minister plenipotentiary to Spain from 1790 to 1794.He was a friend of explorer George Vancouver, who named Mount St.