DemographicsUnderwood (Tas.) is approximately 103.83 square kilometres. In 2016 the population of Underwood (Tas.) was 363. The population is 54% male and 46% female. On average the monthly mortgage repayments in Underwood (Tas.) are $1000 to $1399. The most common weekly income bracket is $800 to $999 per week. Weekly rents in the area are on average $0 to $74.