William Austin Horn (1841–1922) was an Australian mining magnate, pastoralist, politician, author, sculptor and philanthropist. Somewhat eccentric, in 1892 he was the donor of a copy of Antonio Canova's Venus, Adelaide's then controversial first public statue, which is still on display on North Terrace, Adelaide. Horn also built Wairoa, Aldgate, known for its magnificent gardens and captured in a watercolour by William Tibbits.
Horn was born 26 February 1841 at Menaroo (an old name for the Monaro district), New South Wales, to Edward Kirk Horn, a storekeeper, and his wife Emily, née Austin. The family moved to South Australia in 1852, where Horn was educated at the Collegiate School of St Peter.
On 24 September 1879 in St Andrews Church, Walkerville, he married Penelope Elizabeth Belt; they had two daughters and six sons.
In 1896 he sold Wairoa and relinquished all of his official positions in Adelaide. From 1898 he lived at Wimbledon Park House in England. He returned briefly to Adelaide in 1901, and in 1907 to sell his Walkerville house, Holmwood. He held that "an Australian is simply an Englishman born in the sun". He died on 23 December 1922 in London.
Copper deposits had earlier been discovered in the Yorke Peninsula region at Wallaroo, and a further discovery was made nearby in 1861 on the property of pastoralist Walter Watson Hughes. On learning that news of the discovery had been leaked to another party, Hughes dispatched the young William Horn on a 22-hour horse ride to successfully register the claim in Adelaide. This claim became the prosperous Wheal Hughes, at Moonta.
Horn was the member for Flinders in the South Australian House of Assembly from 1887 until 1893.