Ellsworth was founded by Benjamin Milliken and Benjamin Joy in 1763 as Union River Settlement who intended to build dams and sawmills. It was later organized as Plantation 7 and at times called Bodwoin. In 1800 it was incorporated as Ellsworth, named for Oliver Ellsworth, the Connecticut delegate to the 1787 National Convention that was working on a Constitution for the United States of America, and later the 3rd Chief Justice of the Supreme Court. Ellsworth was incorporated by the Maine Legislature in 1869.