Cox's parents moved from Portsmouth to Southampton in the 1840s. His father worked for the Post Office. The 1861 census recorded that Samuel junior followed his father into being a Post Office clerk. In the early 1860s Samuel Cox lived with his parents, six siblings and two nieces, in Clifford Street, St Marys. The 1863 residents section of the Southampton directory included Samuel Cox and Samuel J. Cox junior 'of the Post Office' as residents of Clifford Street.
Samuel John Cox's time as a photographer in Southampton was short. He was listed in the Photographers section of the Southampton Trade Directory in 1865, at 24 Weymouth Terrace. It seems that he left Southampton soon after this time, as the only other trace of Samuel J. Cox found so far is in the 1871 census. A Samuel J. Cox, of the right age and born in Portsmouth, was recorded as a lodger at the Six Bells Inn, Great Waltham, Essex. Samuel J. Cox and another male lodger were listed as workers for the Ordnance Survey. Given the strong connections between the Southampton based Ordnance Survey and photography at that time, it seems very likely that this record was for the same Samuel Cox who advertised as a photographer in Southampton in 1865.