Sir John Francis Fortescue Horner, KCVO, (1842–1927) was a British barrister.
Horner's family were descended from the "Little Jack Horner" referred to in the children's nursery rhyme. The family took possession of Mells Manor in Mells (near Frome), Somerset, at the Dissolution of the Monasteries in the 16th century. He married Frances Graham on 18 January 1883. Through her, he became associated with the social group known as The Souls, several of whom were frequent visitors to Mells, including the Liberal MP H. H. Asquith, who later became prime minister. Horner worked as a barrister in London and served as Commissioner of Woods, Forests and Land Revenues from 1895, for which he was knighted as a Knight Commander of the Royal Victorian Order (KCVO) in 1907.
With Frances, he had four children. Their youngest, Mark, died of scarlet fever in 1908 at the age of 16. Their eldest, Edward was educated at Eton College and Balliol College, Oxford before being called to the bar and beginning a pupilage as a barrister; he joined the British Army at the outbreak of the First World War and was killed at the Battle of Cambrai in France in 1917. Their youngest daughter, Katharine, married Raymond Asquith, the prime minister's son; Raymond was also killed in the First World War. Both Edward and Raymond are commemorated by memorials by Sir Edwin Lutyens in St Andrew's Church, Mells.