We report on a research project into the HCCDA (Historical Census and Colonial Data Archive). The research project has consisted of close reading of the data, consultation with domain experts to assess and clarify the historical context in which the data was originally captured, and the development of an ontological structure (represented in .TTL or Turtle) to represent information in a knowledge graph (in adherence to the RDF or Resource Description Framework abstract data model). We additionally report on a deep dive into data from New South Wales (NSW) focusing on a specific data category -occupations - as expressed in all relevant Censuses (1833 - 1901 inclusive). We have also examined this category longitudinally looking at censuses collected across all of the colonies. For consistency, the longitudinal study has included only those years when the census was collected in all colonies in the same year (1861, 1881, 1891, and 1901).