Osmond Gilles was another founding member of The S.A. Literary Association formed in 1834, and its first treasurer. It was as first Colonial Treasurer that Gilles landed at Holdfast Bay (Glenelg) on the 28th December 1836 from the Buffalo. He remained as Colonial Treasurer until removed from office for incompetence by Governor Gawler in September 1839.
After his retirement, Gilles entered upon pastoral pursuits, and greatly improved the flocks by importing pure Saxon merinos. He opened the Glen Osmond silver-lead mine, and was a member of the syndicate of five who won the ballot for the township of Glenelg. The first ship built in the Patawalonga in November 1839, a cutter of 22 tons called O.G., was named after him as is the O.G. Road.
He died in 1866 aged 79 at Glen Osmond, where he had established the well-known Woodley estate.