Sir John William Jeffcott (1796 – 12 December 1837) was the first judge of the Supreme Court of South Australia.

On Friday, 10 May 1833 a duel with pistols was organised at Haldon racecourse near Exeter, between the two men, in the course of which Hennis was fatally wounded.

The three organisers of the duel were tried as accessories to the murder, but were acquitted, apparently due to a misunderstanding of the applicable law on the part of the jury.

B. Hack and family,[3] his arrangements for passage being made secretly to defeat the efforts of creditors to recover money from him.

He arrived in Hobart, Van Diemen's Land (Tasmania) on 1 January 1837, where he became engaged to marry his cousin Anne Kermode.

His brother William Jeffcott was also a barrister and in 1843 was appointed a judge of the Supreme Court of New South Wales for the District of Port Phillip.