The complexity of large cities such as Sydney makes planning challenging. There is a growing need for new and evolving tools to assist research and decision-making. Increasingly, planners require sophisticated insights on social behaviour and the interdependencies characterising urban systems. Agent-based modelling as a large and wide-spread scientific modelling technique (that focuses on computer modelling of individuals and their interactions) has recently emerged as a promising tool in this regard with applications to real-world problems in infrastructure, particularly transport planning, of urban areas. An essential element of such an agent based model is a realistic synthetic population that matches the distribution of individuals and households living in a study area as per the demographics from census data. This paper presents an algorithm to construct such a synthetic population that uses only aggregated data of demographic distributions as inputs, and an agent based model which simulates the natural evolutions (ageing, marriage, divorce, reproducing) of this initial population. The significance of the synthetic population developed in this work is in its ability to capture the relationship of individuals in a household and changes in structure of households as individuals undergo natural evolutions. A case study that uses the algorithm to initialise a synthetic population for Randwick (Sydney) in 2006 and evolve this population over 5 years will also be presented. The results of the initial and final population were validated against the Census Data in 2006 and 2011. The paper closes with discussions on the application of this synthetic population to simulate the dynamics interaction between transport and land-use.