Bordered by West Virginia, Virginia, Tennessee, Missouri, Illinois, Indiana, and Ohio, Kentucky is situated in the Upland South. Its northern border is formed by the Ohio River and its western border by the Mississippi River. Originally a part of Virginia, in 1792 Kentucky became the 15th state to join the Union. It is known as the "Bluegrass State", a nickname based on the bluegrass found in many of its pastures due to fertile soil. One of the major regions in Kentucky is the Bluegrass region in central Kentucky which houses two of its major cities, Louisville and Lexington, and also the capital city, Frankfort.