Milton, John Francis was never an Australian, but from the United Kingdom, as confirmed by the 1860 census record. He was a convict in Tasmania, sent there in 1844, and was supposed to have been married in 1852, but there is no record of this marriage in the indices. As well, his wife would have only been aged about 11 or 12 in that year, so there is a possibility that they probably eloped and went to live in the United States.
However, there is a record of her marriage, in Tasmania, to Alexander Wannan, in 1867, two years after the death of John Francis, so it is obvious that she had decided to return home to where her family were, instead of remaining in the U.S.
John Fearn/Francis' residence in Australia was very brief, being perhaps a matter of about eight or ten years, and as a convict, so he was no more an Australian than several other Civil War veterans, who were born elsewhere, but lived here briefly before returning to the United States, the United Kingdom or even Germany (this last one refers to Otto Hagen, an officer in a New York regiment, born in Germany, served in the Civil War, lived in Queensland for about 25 years, but returned to Germany where he died).