Clarksville is a town in Clark County, Indiana, United States, along the Ohio River and is a part of the Louisville Metropolitan area. The population was 21,724 at the 2010 census. The town was founded in 1783 by early resident George Rogers Clark at the only seasonal rapids on the entire Ohio River, it is the oldest American town in the former Northwest Territory. The town is home to the Colgate clock, one of the largest clocks in the world and the Falls of the Ohio State Park, home to the world's largest exposed Devonian period fossil bed.
The site that would become Clarksville was first used as a base of operations by George Rogers Clark during the American Revolution. In 1778 he established a post on an island at the head of the Falls of the Ohio, from which he trained his 175-man regiment for the defense to the west. After the war, Clark was granted a tract of 150,000 acres (610 km2) for his services in the war. In 1783, 1,000 acres (4 km2) were set aside for the development of a town, Clarksville. The same year a stockade was built and settlement began.
The explorer William Clark was a younger brother of George Rogers Clark. Renowned historian Stephen Ambrose writes of Meriwether Lewis and William Clark in Undaunted Courage, "When they shook hands [at Clarksville], the Lewis and Clark Expedition began." A two-figure statue near the falls commemorates the expedition.