The Madison River is a headwater tributary of the Missouri River, approximately 183 miles (295 km) long, in Wyoming and Montana. Its confluence with the Jefferson and Gallatin rivers near Three Forks, Montana forms the Missouri River. The river was named in July 1805 by Meriwether Lewis at Three Forks. The central fork of the three, it was named for U.S. Secretary of State James Madison, who would succeed Thomas Jefferson as President in 1809. The western fork, the largest, was named for President Jefferson and the east fork for Treasury Secretary Albert Gallatin.