District of Maine

Maine, the 23rd state in America, did not gain statehood until 15 March 1820. Prior to that, it was called the District of Maine and belonged to the state of Massachusetts. According to Maine History, Maine's statehood was granted by Congress "under the Missouri Compromise of 1820. This arrangement allowed Maine to join the Union as a free state, with Missouri entering a year later as a slave state, thereby preserving the numerical balance between free and slave states in the nation."