High Quality Content by WIKIPEDIA articles! Waldo County is a county located in the U.S. state of Maine. As of 2000, the population was 36,280. Its county seat is Belfast. According to the U.S. Census Bureau, the county has a total area of 853 square miles (2,209 km²), of which, 730 square miles (1,890 km²) of it is land and 123 square miles (319 km²) of it (14.43%) is water.There were 14,726 households out of which 30.70% had children under the age of 18 living with them, 55.20% were married couples living together, 9.00% had a female householder with no husband present, and 31.70% were non-families. 24.90% of all households were made up of individuals and 9.60% had someone living alone who was 65 years of age or older. The average household size was 2.43 and the average family size was 2.88.