James Knox Polk ( November 2 , 1795 â `` June 15 , 1849 ) was the eleventh President of the United States , his term was from March 4 , 1845 to March 3 , 1849 . James Knox Polk ( ; November 2 , 1795 -- June 15 , 1849 ) was the 11th President of the United States ( 1845 â `` 1849 ) .