DemographicsLake St Clair is approximately 840.46 square kilometres. In 2016 the population of Lake St Clair was 4. The population is 50% male and 50% female. On average the monthly mortgage repayments in Lake St Clair are $0 to $299. The most common weekly income bracket is $0 to $149 per week. Weekly rents in the area are on average $0 to $74.