DemographicsSt Helens Plains is approximately 134.42 square kilometres. In 2016 the population of St Helens Plains was 42. The population is 52% male and 48% female. On average the monthly mortgage repayments in St Helens Plains are $0 to $299. The most common weekly income bracket is $150 to $299 per week. Weekly rents in the area are on average $0 to $74.