The size of Millbrook is approximately 9.5 square kilometres. The population of Millbrook in 2011 was 535 people. By 2016 the population was 110 showing a population decline of 79.4% in the area during that time. The predominant age group in Millbrook is 40-49 years. Households in Millbrook are primarily couples with children and are likely to be repaying under $300 per month on mortgage repayments. In general, people in Millbrook work in a trades occupation. In 2011, 90.2% of the homes in Millbrook were owner-occupied compared with 84.8% in 2016.