He was baptised William Charles Cox at St Phillip's Church, Sydney, with the surname of his mother, as his parents William Charles Wentworth I and Sarah Cox were not legally married until 1829. NSW BDM Birth Index Numbers 115/1827 V1827115 12 and 8388/1827 V18278388 1C refer to him.

William attended Sydney College until the age of 15, and in his final exams won the school medal for classics. In February 1844 he sailed to England (aboard the ship Palestine) to continue his education. He was sent to a private tutor for a year or two before entering Trinity College, Cambridge. He commenced legal studies with Middle Temple in 1849, but discontinued them in 1852. The Wentworth family re-located to England in 1853. In 1855, Willie and his aunt's step-daughter, Amelia Hunt, re-acquainted whilst her family were visiting England, and they began courting. However, her father required that William must complete his legal studies before any relationship could proceed. He re-entered Middle Temple and kept lodgings at Norfolk Street, and by 1857 he was working in a legal office. He was called to the Bar in June 1858.

By late 1858, William's health was extremely poor, with him experiencing both a mental and physical breakdown. His mother took him to St John's Wood, a more relaxing environment; doctors visited him daily. He passed away at 5 Loudoun Road, St John's Wood on 31 March 1859 and was buried 6 April 1859 in the West of London and Westminster Cemetery at Old Brompton, London.

DEATH NOTICE

"WENTWORTH—March 31st, at the residence of his father, Loudon Road, St. John's Wood, London, aged 31 years, William Charles, eldest son of W. C. Wentworth, Esq."

The Sydney Morning Herald, Wed 13 Jul 1859, Page 7.

trove.nla.gov.au/newspaper/article/13027649

After his father died, in March 1872, his mother commissioned the construction of a mausoleum in Sydney and organised for the repatriation of the remains of her husband, her son William, and daughters Sarah and Isabella, all of whom had died outside Australia. William's remains were removed from Old Brompton on 11 January 1873, and reinterred in the newly built mausoleum on the family's property at Vaucluse NSW.

More biographical details may be found in the following book:

Liston, Carol, Sarah Wentworth: Mistress of Vaucluse, (Historic Houses Trust of New South Wales, Glebe, New South Wales, 1988). ISBN 0 949753 34 3.