William was born at "Millbrae", Native Valley, near Nairne, South Australia, the son of Richard Mills the younger (1840–1870). He took over his father"s farm around 1880 and continued breeding Merino sheep with some success, purchasing valuable rams from Alick J. Murray, and expanded the farm from 500 to 5,000 acres (200 to 2,020 ha), including "Bondleigh" farm, later held by his eldest son, W. Champion Mills.
He was educated at Nairne public school and Review A. Law"s grammar school at Mount Barker.
He gained experience as a jackaroo for Robert Browne, manager of Winnininnie Station in the north of the State. This Association was to become the nucleus of the Country Party in South Australia. In 1918 he successfully stood for a Northern district seat in the South Australian Legislative Council, and held that seat until 1933, when he declined to stand due to poor health.
Everlina (1883–1961) married Hugh Ross Patterson on 12 April 1906.
West. Champion Mills (ca1885 – 20 May 1941)
R(ichard) Surguy Mills (ca1886 – 26 October 1944) married Barbara Mary
Jack Mills (ca1889 – 11 April 1917) fought with the 11th Battalion in World War I and died in Rouen of war injuries. Margaret Mills, nursing sister at Portuguese Augusta Hospital
Alec Mills (ca1892 – ) married Phoebe M. Blacket on 29 October 1919.
Thomas Bruce Mills (1894 – 12 August 1915) enlisted for overseas service, but died in Adelaide of meningitis, complication of measles. Lizzie (1900 – ) married Ronald R. Loveday of Renmark on 27 August 1924.
Most members of the family were buried at Blakiston cemetery.
