Lt. Jonathon Warner was an army officer employed as a surveyor on the Great North Road until 1829.
In April 1828, he was sent with John McDonald to check out his alternative line for the Great North Road. He had trouble with the convicts in his charge and found shortages of supplies and comforts out in the bush trying.
The quality of work done by the convicts under his supervision is generally considered rather rough, especially when compare with the work they did for Percy Simpson who replaced him in 1829. In 1830, he retired from roadworks and took up a land grant on Lake Macquarie, now called Warner’s Bay. From this time, he worked as a magistrate in the Gosford area, riding there regularly from his Lake Macquarie home.