Arthur Annesley, 1st Earl of Mountnorris FRS (7 August 1744 - 4 July 1816) was an Irish peer.
He was the son of Richard Annesley, 6th Earl of Anglesey, and the Countess Juliana Donovan, who belonged to the junior sept of the O'Donovans of Clan Loughlin, the Donovans of Ballymore in County Wexford. She was initially rumoured to be of lower birth, the ancient pedigrees of some Irish families not being widely known in the English-speaking world at that time, and hers deriving from a remote region of Ireland, the Barony of Carbery. The Countess Juliana was the great-great-great-granddaughter of Donel Oge na Cartan O'Donovan, the 1st Lord of Clan Loughlin to hold his territories from the Crown, from 1616 (see surrender and regrant).
He married, Lucy Lyttelton, daughter of George Lyttelton, 1st Baron Lyttelton of Frankley, and Lucy Fortescue, on 10 May 1767. They had, among other children:
He next married Sarah Cavendish, daughter of Sir Henry Cavendish, 2nd Baronet, and Sarah Bradshaw, 1st Baroness Waterpark, on 20 December 1783. They had, among other children:
He succeeded to the title of 6th Baron Altham, of Altham, in County Cork, and to the title of 8th Viscount Valentia upon his father's death on 14 February 1761.
On 22 April 1771, the House of Lords decided that his claim to his father's English titles was not valid, and that therefore these titles had become extinct on his father's death in 1761. He was created 1st Earl of Mountnorris [Ireland] on 3 December 1793.