This is a list of the sixteen counties in the U.S. state of Maine. Prior to statehoo, Maine was officially part of the state of Massachusetts and was called the District of Maine. Maine was granted statehood on March 15, 1820 as part of the Missouri Compromise. Nine of the sixteen counties had their borders defined while Maine was still part of Massachusetts, and hence are older than the state itself. Even after 1820, the exact location of the northern border of Maine was disputed with Britain, until the question was settled and the northern counties took their final, official form by treaty in 1845. Almost all of Aroostook County was disputed land until the treaty was signed.