DemographicsMountain River is approximately 25.05 square kilometres. In 2016 the population of Mountain River was 559. The population is 51% male and 49% female. On average the monthly mortgage repayments in Mountain River are $1400 to $1799. The most common weekly income bracket is $400 to $499 per week. Weekly rents in the area are on average $225 to $275.