On 18 September 1856, a year after he arrived from Scotland, he married Elizabeth Clark in Melbourne, Australia. She had arrived three days before the wedding with her maid on the Admiral, the same ship on which he had travelled out a year earlier, which reached Hobsons Bay (Melbournes port) on 15 September 1856, having set sail from London on 7 June 1856. Elizabeth Clark was probably born on 7 October 1832 in Barony parish Scotland, near Glasgow (her mother being Mary McGregor). She was the second daughter of John Clark, of Levenfield House in Alexandria, the Vale of Leven, a short distance north of Glasgow in West Dunbartonshire. His Levenfield Works were involved in similar work to Dr John Macadams father William Macadam in Kilmarnock in the then lucrative business of textile printing for domestic and European markets. The Clarks and Macadams must have become known to each other in Scotland because of their respective fathers business connections. Elizabeth died in 1915, in Brighton, Victoria.
John and Elizabeth had two sons:
John Melnotte Macadam was born 29 August 1858 at Fitzroy, Melbourne, Australia, and died on 30 January 1859, aged 5 months (he was reburied with his father, whose monument bears the additional inscription: In memory of his only children John Melnotte Macadam Born August 29, 1858 Died January 30, 1859 followed by an inscription to his second son below it).
William Castlemaine Macadam was born on 2 July 1860 and died 17 December 1865 at Williamstown, Victoria, Australia. He died aged five and had survived his father by a few months. The inscription on his fathers burial monument under His only children has him listed under his elder brother (above), who died in infancy, but does not for some reason give Williams date of death on it.