Although there is plenty of extrinsic evidence that corroborates the New York Cumorah as explained in Letter VII, there are also incidents in Church history that corroborate Letter VII.
One is a spiritual account provided by Benjamin Benson in 1839. The Joseph Smith Papers provide a useful historical background. However, their footnotes
Historical Background from the Joseph Smith Papers provides useful context:
During his fall 1837 visit to , Missouri, JS spoke with Missouri member Benjamin Benson on the evening of 11 November. At JS’s request, Benson wrote a letter the next day recounting a “dream or vision” he had shared with JS the previous night. The original letter is not extant, but copied Benson’s letter into JS’s second letterbook in 1839.
The account of his dream reveals that, like many of his era, Benson was concerned about the origins of American Indians and the validity of the Bible’s account of human origins. Benson had prayed to learn whether Indians had been placed on the American continent at the creation of the world or had descended from Adam, as he understood the Bible taught. The dream he related to JS occurred forty-two years earlier, in 1795, when he was twenty-two years old. In Benson’s account of the dream, an took him to a specific place where a record was deposited. There the angel showed him a book, which was to come forth at a later time, that contained a record of a people from Jerusalem, who were the forefathers of the American Indians. Benson also saw in his dream a man who would bring forth that book. In the letter, Benson mentions the “Book [of] Ether” from the Book of Mormon, which along with other details indicates he likely felt that the book in the dream was the Book of Mormon and that the man bringing forth the book in his vision was JS.
This link goes to the copy of the letter in the Letterbook 2. I show the notes below, with some brief commentary. My emphasis in bold.
Dear Brother in the Lord, Having reflected on the short interview we had last evening respecting the dream (or vision as you may think proper to term it) and as you stated several times that you should like to have it wrote so that you could take it home with you to , I therefore consent to give a statement in as short <a> manner as I can, without going into every minute circumstance. To wit.—In the year 1795, I then being in the Town of Pompey, County of Onondagua and State of New York; I then being 22 years old; seeing and viewing the ancient Indian Forts and trates thereof through that part of the Country; my mind was anxiously led to contemplate and reflect on where these those Indians came from, or from what race of People they sprang from, and oftentimes heard it stated that these Indians were natives of this Continent, and that they were created and placed here at the creation of the world. Then said I the Bible cannot be true, part of for it (The Bible) says that all the human family sprang from Adam &c, and that all at the time of the flood, the whole earth was covered with water, and that all flesh died, except what were in the ark with Noah, then with things taking place, and I firmly believing that the Bible was true, my heart’s desire was to God in solemn prayer to know where and what race of people these Indians sprang from, It was made known (whether by dream or vision I will leave that for you, to judge) An as I thought came to me and said, Come along with me and I was immediately on a beast like a horse, and the angel at my left hand with his feet about the same height that my feet were as I sat on the horse, and in this position was conveyed to near the place where the record was deposited and he said stop here, and the angel went about 4 or 5 Rods and took in his hand a book, and on his return to where I stood, as I thought there were many stood with me; One said, what book is that? and the answer was, it is a bible a bible, the word of God, a record of a people that came from Jerusalem, the fore fathers of these Indians, And it also contains a record of a people that came from the Tower of Babel at the time the Lord confounded the language and scattered the people into all the world, and it the Book Ether; and then with great anxiety of heart I asked if I might have the book, and answer was that it was not the Lords time then, but it should come, “and you shall see it,” and then said look, and as I looked, I beheld a man standing as I thought at a distance of two hundred yards, and the angel said “there is the Man that the Lord hath appointed &c, and he is not yet born.[”] I have related it in short, as I have not time now to give a full detail of all that I had a view of. Yours with respect.Benjamin BensonNovember 12th 1837Joseph Smith Jr. .N. B At some further time if the Lord will I will be more full if you should wish it. I shall direct this to you as a letter and you cannot act your Judgement in either keeping it to yourself or publishing it by making use of my name.
Note 1: Benson may have been referring to the fortified villages or traditional longhouses built by the Oneida and Onondaga tribes of the Iroquois Six Nations in central New York. He also may have seen forts built during the French and Indian War, some of which were constructed on the ruins of American Indian villages. The forts described by Benson also may have had connections to other indigenous people. Contemporary accounts identified several mounds in western New York and associated these mounds and their fortifications with an ancient moundbuilding people. (Hauptman, Conspiracy of Interests, 27–33, 78, 107; Hamilton, French and Indian Wars, 161–184, 239–249; Vogel, Indian Origins and the Book of Mormon, 24–30.)
Hauptman, Laurence M. Conspiracy of Interests: Iroquois Dispossession and the Rise of New York State. Syracuse, NY: Syracuse University Press, 1999.
Hamilton, Edward Pierce. The French and Indian Wars: The Story of Battles and Forts in the Wilderness. Garden City, NY: Doubleday, 1962.
Vogel, Dan. Indian Origins and the Book of Mormon: Religious Solutions from Columbus to Joseph Smith. Salt Lake City: Signature Books, 1986.
This note doesn't mention the presence of dozens of Ohio Hopewell sites in Western New York dating to Book of Mormon timeframes. Instead, it cites Dan Vogel's book which claims Joseph Smith relied on the "Moundbuilder myth." I refer to this line of reasoning as the "myth of the moundbuilder myth."
Note 2: The theory of polygenism, or different origins for different races, emerged in European scholarly thought in the sixteenth century. As Europeans encountered new cultures and races, polygenism attempted to explain their origins. Discussions of this theory were particularly widespread in the eighteenth and nineteenth centuries as Enlightenment thought led to the development of racial science and the categorization and ranking of different races. Some scholars tried to make the Bible compatible with polygenism, creating theories of multiple or simultaneous creations besides the creation of Adam. Polygenism and its underlying racial concerns are found throughout nineteenth-century popular and religious literature. For many nineteenth-century Christians, the theory was a direct challenge to Christianity’s single biblical creation and the religious requirement of redemption after the fall of Adam and Eve. JS, like other Christians of his day, emphasized the single creation found in the Bible and humanity’s common descent from Adam and Eve. (Kidd, Forging of Races, 121–167; Livingstone, Adam’s Ancestors, 169–201; Reeve, Religion of a Different Color, 131.)
Kidd, Colin. The Forging of Races: Race and Scripture in the Protestant Atlantic World, 1600–2000. Cambridge: Cambridge University Press, 2006.
Livingstone, David N. Adam’s Ancestors: Race, Religion, and the Politics of Human Origins. Baltimore: Johns Hopkins University Press, 2008.
Reeve, W. Paul. Religion of a Different Color: Race and the Mormon Struggle for Whiteness. Oxford: Oxford University Press, 2015.
Note 3. See Book of Mormon, 1830 ed., 539 [Ether 1:33–35]; and Title Page of the Book of Mormon, ca. Early June 1829.
Note 4. The letter was not published in either the Elders’ Journal or the church’s later publication, Times and Seasons.
Glenn Rawson did a short video on this letter: