The Ohio River marks Kentucky's northern border with Ohio, Indiana and Illinois (more than 600 miles).
In his Notes on the State of Virginia published in 1781-82, Thomas Jefferson stated: "The Ohio is the most beautiful river on earth. Its current gentle, waters clear, and bosom smooth and unbroken by rocks and rapids, a single instance only excepted." That one exception is the Falls of the Ohio at Louisville, Kentucky. The falls is a 2.2-mile-long limestone rapids where the river drops 23.9 feet. Canalization around the rapids was completed in 1830, ensuring navigability.
Five major Kentucky cities lie on the Ohio: Ashland, Covington, Louisville, Owensboro, and Paducah.