DemographicsMarion Bay (Tas.) is approximately 4.1 square kilometres. In 2016 the population of Marion Bay (Tas.) was 72. The population is 50% male and 50% female. On average the monthly mortgage repayments in Marion Bay (Tas.) are $1800 to $2399. The most common weekly income bracket is $300 to $399 per week. Weekly rents in the area are on average $225 to $275.