The Book of Mormon land is in the US and not in South America
Theory that many support
Although evidence does not 100% validate this theory, there are many who believe it. A good book to read about this subject is "This Land: They Came From the East" by Wayne N. May. May claims that the events told in the Book of Mormon took place in the northeastern area of the United States.
Joseph Smith also seemed to believe that the United States was the Book of Mormon land. He revealed the site of the ancient Manti city to be near Huntsville, Missouri (History of JS, Vol 16, pg 296) Smith also once identified some bones found in Illinois during the Zion's Camp march to be the bones of a Lamanite whose name was Zelph and who had died in one of the last battles.
Of course, there is also evidence, good theory and Joseph Smith quotes that places the events in Central America. The final verdict - we don't know for sure.