In the context of low fertility and population ageing, many countries will look to immigration to address shortages in labour and reduce the effects of population decline. While the short-term effects of immigration are relatively well understood, the long-term demographic consequences of high and sustained levels of immigration are still to be determined. In Australia, the dismantling of racially discriminatory migration policies in the 1970s and introduction of the subsequent large-scale migration program provides analysts with an opportunity to better understand the impacts of immigration. In this paper, we highlight the major contributions that immigration has made towards population change across eleven geographic areas in Australia from 1981 to 2021. The analyses utilise recently reconciled demographic component data for 18 different immigrant groups and the Australia-born population by age and sex. While net international migration of overseas-born persons contributed approximately 56% of overall population growth over the 40-year period, there were also sizeable contributions made by immigrants to other demographic processes, including 28% of births, 31% of deaths, and 18% of interregional migration. This research provides new insights into both the period-specific and long-term demographic effects of diverse immigration streams across state capital cities and regional areas in Australia.