The area of Virginia was part of the original territory of the United States. Virginia was the first chartered colony, with the original 1606 charter including the entire Eastern Seaboard. Individual charters provided to other colonies reduced the size of Virginia. In 1784, Virginia ceded area to the United States that became the Northwest Territory in 1787. Virginia ratified the U.S. Constitution on June 26, 1788; it was the tenth of the original 13 states to join the Union. At the time of statehood, Virginia included all of present-day Kentucky and West Virginia. The area of the state was reduced in 1791 by the formation of the District of Columbia and in 1792 when Virginia ceded the area that became the state of Kentucky. Virginia added territory in 1846 when the portion of the District of Columbia taken from Virginia was retroceded to the state. The state of West Virginia, consisting of 48 counties, was established from Virginia on June 20, 1863; in 1866, Congress officially added two more counties (Berkeley and Jefferson) to West Virginia, leaving Virginia with generally the same boundary as the present state. Virginia is one of four states that are legally described as a commonwealth.