There are 19 US Post Offices in Waldo County serving a total of 38,829 residents equating to 2,044 residents per post office. It's estimated that approximately 61,975 packages are handled across the 19 county post offices annually. Waldo County is a county located in the state of Maine, in the United States. As of the 2010 census, the population was 38,786. Its county seat is Belfast. The county was founded on 7 February 1827 from a portion of Hancock County and named after Brigadier-General Samuel Waldo, proprietor of the Waldo Patent.