William Hay, 19th Earl of Erroll

William Harry Hay, 19th Earl of Erroll (3 May 1823 – 3 December 1891), styled Lord Hay between 1823 and 1831, and Lord Kilmarnock from 1831 to 1846, was a Scottish peer.

Early life William Harry Hay was born on 3 May 1823. He was the only son of four children born to Lady Elizabeth FitzClarence and William Hay, 18th Earl of Erroll. His elder sister, Lady Ida Hay, married Charles Noel, 2nd Earl of Gainsborough (her descendants include the Earls of Gainsborough, the Marquesses of Bute and the Baronets of Bellingham). His younger sisters were Lady Agnes Hay, wife of James Duff, 5th Earl Fife (her son, Alexander Duff, 1st Duke of Fife, married Princess Louise, daughter of King Edward VII), and Lady Alice Hay, who married Charles Edward Louis Casimir Stuart, Count d'Albanie (nephew of fraud John Sobieski Stuart).

His paternal grandparents were William Hay, 17th Earl of Erroll and, his second wife, the former Alicia Eliot (third daughter of Samuel Eliot of Antigua). His maternal aunts and uncles were George FitzClarence, 1st Earl of Munster, Henry FitzClarence, Sophia FitzClarence (wife of Philip Sidney, 1st Baron De L'Isle and Dudley), Mary FitzClarence (wife of Charles Richard Fox), Lord Frederick FitzClarence, Lord Adolphus FitzClarence, Augusta FitzClarence, Lord Augustus FitzClarence, and Amelia FitzClarence (wife of Lucius Cary, 10th Viscount Falkland).

Career Lord Erroll served as the third Page of Honour from 1832 to 1839 (for his grandfather, King William IV, from 1832 to 1837, and for Queen Victoria, his grandfather's niece, from 1837 to 1839). and the former Sarah Rachel Fraser (eldest daughter of James Fraser, a member of the Council of Nova Scotia). The Countess of Erroll served as a Lady of the Bedchamber to Queen Alexandra (wife of King Edward VII) beginning in 1872. Together, they were the parents of seven children: he was awarded CVO.