William Cunningham, 9th Earl of Glencairn (Scottish Gaelic: Uilleam Coineagan) (1610–1664), was a Scottish nobleman, Lord Chancellor of Scotland, and a cavalier. He was also the chief of Clan Cunningham. The eldest son of William Cunningham, 8th Earl of Glencairn, on 21 July 1637 this William obtained a ratification from King Charles 1st, under the Royal Sign Manual, of the original Glencairn Letters Patent of 1488. He was sworn a member of the Privy Council of Scotland and in 1641 was appointed a Commissioner of the Treasury.