[2][6] His son James died six months later; he drowned while droving cattle across Kyabra Creek at Euroongoola Station in Western Queensland on 27 February 1887 aged 21 years.

[2] Having lost both wives, John Sinclair spend his later years in poor health, living at his home, Delholm, at 393 Main Street, Kangaroo Point, attended by a housekeeper, a groom and a male nurse.

[9][10] John Sinclair died at Kangaroo Point, Brisbane on 5 May 1906 aged 78 years[2] and was buried in Toowong Cemetery, together with his second wife Constance and his two of his adult children Margaret and James.

[10] John Sinclair was an alderman of the Brisbane Municipal Council for the ward of Kangaroo Point from 1871[12] until 1874 when he retired.

Assisted by his daughters Jessie and Margaret, John Sinclair entertained the royal party at a ball in the old Exhibition Building, a function of great brilliance.