The study of immigrant population change is hindered by data sources that capture international migration flows separately from other demographic process and population stock data. In this paper, we illustrate this by gathering detailed demographic data and estimates for the Australia-born population and 18 immigrant populations in Australia, according to their country or region of birth. We then develop a methodology for reconciling differences in these data sets to study the sources of quinquennial immigrant population change from 1981 to 2016 by age, sex, and geographic area. Reconciliation refers to the process of ensuring consistency between the demographic components of change (i.e., births, deaths and migration) and total population change. We validate the methodology by how well it predicts the population 5 years later by age and sex using a multiregional cohort-component prediction model. Once the data are reconciled for every 5-year period from 1981 to 2016, we then see how well the reconciled data reproduces the 2016 population data using the 1981 population as a starting point. This research is useful for improving our understanding of the mechanisms and subsequent spatial contributions of immigration to population change over time. We demonstrate such value by examining the reconciled sources of regional population change for populations born in Australia, the United Kingdom and China over time.