William Beresford, 1st Baron Decies (16 April 1743 – 6 September 1819) was an Anglo-Irish clergyman. Decies was the third son of Marcus Beresford, 1st Earl of Tyrone, and Catherine Poer, 1st Baroness de la Poer. George Beresford, 1st Marquess of Waterford, was his elder brother. He served as Bishop of Dromore from 1780 to 1782, Bishop of Ossory from 1782 to 1794, and as Archbishop of Tuam from 1794 until his death in 1819. He was admitted to the Irish Privy Council in 1794 and in 1812 he was raised to the Peerage of Ireland as Baron Decies, of Decies in the County of Waterford.