The United States nearly doubled in size with the Louisiana Purchase. The staggering purchase price of fifteen million dollars was actually a bargain, as it amounted to about four cents per acre. Once the purchase was finalized, the next question was: what did the United States actually buy? President Thomas Jefferson tasked Meriwether Lewis with exploring the land west of the Mississippi to the Pacific Ocean. Lewis chose William Clark as his co-leader. The Corps of Discovery set off from Camp Dubois, outside of St. Louis, Missouri, on May 14, 1804. It would be two years before they returned.