Louisville is the largest city in the Commonwealth of Kentucky and the 28th most populous city in the United States. It is the state's only designated first-class city. Louisville is the historical seat and, since 2003, the nominal seat of Jefferson County.Lousville was founded in 1778 by George Rogers Clark and is named after King Louis XVI of France, making Louisville one of the oldest cities west of the Appalachian Mountains. Sited beside the Falls of the Ohio, the only major obstruction to river traffic between the upper Ohio River and the Gulf of Mexico, the settlement first grew as a portage site. It was the founding city of the Louisville and Nashville Railroad, which grew into a 6,000-mile (9,700 km) system across 13 states. Today the city is known as the home of the Kentucky Derby, Kentucky Fried Chicken, the University of Louisville and its Louisville Cardinals athletic teams, Louisville Slugger baseball bats, and three of Kentucky's six Fortune 500 companies. Its main airport is also the site of UPS's worldwide air hub.