High Quality Content by WIKIPEDIA articles! Mark Twain Lake is located in Ralls County, Missouri and Monroe County, Missouri. It was created by the Clarence Cannon Dam impounding the Salt River and is located about twenty miles (32 km) southwest of Hannibal. It was named for Missouri author Mark Twain and part of the area around it is Mark Twain State Park. The village of Florida is located next to the lake and was the site of Twain`s birth.