Kentucky (US: , UK: ), officially the Commonwealth of Kentucky, is a landlocked state in the Southeastern region of the United States. It borders Illinois, Indiana, and Ohio to the north, West Virginia to the northeast, Virginia to the east, Tennessee to the south, and Missouri to the west. Its northern border is defined by the Ohio River. Its capital is Frankfort and its most populous city is Louisville. As of 2020, the state's population was approximately 4.5 million. Previously part of Virginia, Kentucky was admitted into the Union as the fifteenth state on June 1, 1792. It is known as the "Bluegrass State" in reference to Kentucky bluegrass, a species of grass introduced by European settlers which has long supported the state's thoroughbred horse industry. The fertile soil in the central and western parts of the state led to the development of large tobacco plantations similar to those in Virginia and North Carolina, which utilized enslaved labor prior to the passage of the Thirteenth Amendment. Kentucky ranks fifth nationally in goat farming, eighth in beef cattle production, and fourteenth in corn production. While Kentucky has been a long-standing center for the tobacco industry, its economy has diversified into non-agricultural sectors including auto manufacturing, energy production, and medicine. Kentucky ranks fourth among US states in the number of automobiles and trucks assembled. It is one of several states considered part of the Upland South. The state is home to the world's longest known cave system in Mammoth Cave National Park, the greatest length of navigable waterways and streams in the contiguous United States, and the nation's two largest artificial lakes east of the Mississippi River. Cultural aspects of Kentucky include horse racing, bourbon, moonshine, coal mining, My Old Kentucky Home State Park, automobile manufacturing, tobacco, Southern cuisine, barbecue, bluegrass music, college basketball, Louisville Slugger baseball bats, and Kentucky Fried Chicken.