DemographicsPlainby is approximately 38.42 square kilometres. In 2016 the population of Plainby was 44. The population is 48% male and 52% female. On average the monthly mortgage repayments in Plainby are $1000 to $1399. The most common weekly income bracket is $150 to $299 per week. Weekly rents in the area are on average $0 to $74.