JS talks about historicity of the Book of Mormon.
Joseph Smith, Letter to John M. Bernhisel, November 16, 1841, Joseph Smith Papers website, accessed July 26, 2021, The Joseph Smith Papers website, accessed August 11, 2021
I received your kind present by the hand of Er Woodruff & feel myself under many obligations for this mark of your esteem & friendship which to me is the more interesting as it unfolds & developes many things that are of great importance to this generation & corresponds with & supports the testimony of the Book of Mormon; I have read the volumes with the greatest interest & pleasure & must say that of all histories that have been written pertaining to the antiquities of this country it is the most correct luminous & comprihensive.