DemographicsSt Marys (Tas.) is approximately 192.04 square kilometres. In 2016 the population of St Marys (Tas.) was 682. The population is 52% male and 48% female. On average the monthly mortgage repayments in St Marys (Tas.) are $1000 to $1399. The most common weekly income bracket is $400 to $499 per week. Weekly rents in the area are on average $0 to $74.