Millbrook is a rural district in the state of Victoria, Australia, located 90 kilometres (56 mi) north west of Melbourne. It was formerly called "Moorabool" but the name was changed to avoid confusion with a locality near Geelong. The name "Millbrook" was adopted because of a flour mill erected by Matthew Butterly on the West Moorabool creek. At the time of the 2011 census, Millbrook had a population of 359, down from 550 in 2006, partly reflecting changing boundaries. The soil is volcanic and well-adapted to cereals, potatoes and grazing. The landscape is undulating and preserves remnants of the original open forest. The West Moorabool creek runs through the district. The earliest inhabitants of the area were the Wathaurong, and the Irish were prominent among its European settlers in the mid nineteenth century.