High Quality Content by WIKIPEDIA articles! The Cumberland River is a waterway in the Southern United States. It is 688 miles (1,107 km) long. It starts in Harlan County in far southeastern Kentucky between Pine and Cumberland mountains, flows through southern Kentucky, crosses into northern Tennessee, and then curves back up into western Kentucky before draining into the Ohio River at Smithland, Kentucky. The city of Nashville, Tennessee sits along the banks of the Cumberland River.