Waldo County is a county in the state of Maine, United States. As of the 2020 census, the population was 39,607. Its county seat is Belfast. The county was founded on February 7, 1827, from a portion of Hancock County and named after Brigadier-General Samuel Waldo, proprietor of the Waldo Patent.

Somerset County is a county in the U.S. state of Maine, United States. As of the 2020 census, the population was 50,477. Its county seat is Skowhegan.