Hornung was born Ernest William Hornung on 7 June 1866 at Cleveland Villas, Marton, Middlesbrough; he was nicknamed Willie from an early age. He was the third son, and youngest of eight children, of John Peter Hornung (1821-86) and his wife Harriet née Armstrong (1824-96). John was christened Johan Petrus Hornung in the Transylvania region of Hungary and, after working in Hamburg for a shipping firm, had moved to Britain in the 1840s as a coal and iron merchant. John married Harriet in March 1848, by which time he had anglicised his name. At the age of 13 Hornung joined St Ninian's Preparatory School in Moffat, Dumfriesshire, before enrolling at Uppingham School in 1880. Hornung was well liked at school, and developed a lifelong love of cricket despite limited skills at the game, which were further worsened by bad eyesight, asthma and, according to his biographer Peter Rowland, a permanent state of generally poor health.