Population census data in Croatia is provided in spreadsheet and without explicit geometric representation of its spatial units which makes it not directly usable in spatial analyses and data-based decision-making. This poses challenges for data interoperability and limits practical usefulness of census data. To overcome these limitations, this paper aims to propose ontology mapping schema to structure population contingents by age and sex in RDF and publish it as Linked Open Data using open-source data wrangling tool, OpenRefine. In line with Linked Data best practices, population data and spatial units’ geometries were modelled separately and linked through spatial unit’s URIs. Also, to ensure interoperability and enable broader integration, the schema reuses semantics from RDF Data Cube Vocabulary and GeoSPAQRL while the use of open technologies ensures that the resulting RDF triples are reproducible. This proposed ontology mapping schema represents a foundational step towards the publication of linked open census data in Croatia, paving the way for improved integration and reuse in the future.