Letter VII was his last word on the subject.
Letter VII was explicit and unambiguous: the New York hill where Joseph obtained the plates was the hill Cumorah in the Book of Mormon. The mile-wide valley to the west of the hill was the location of the final battles of the Nephites and Jaredites took place. No one who reads Letter VII can be mistaken about this. There is no room for confusion about this point.
Why would Joseph have to say anything more on the topic?
The geography issue is more straightforward than people think. Letter VII is by far the most specific and declarative statement about Book of Mormon geography in existence. Although it was written by Oliver Cowdery, Joseph helped write it and explicitly endorsed it multiple times.
Everything directly attributable to Joseph Smith is consistent with Letter VII and the North American geography. Everything that contradicts Letter VII and the North American geography is not directly attributable to Joseph Smith.
Another way to say it: Those who think Joseph didn't know where the Book of Mormon took place rely on statements that can't be directly attributed to him.
I'll address objections to Letter VII in a separate post. Here, I want to point out that after Letter VII, Joseph wrote or said only three known things about the geography question, all of which are consistent with Letter VII. These are the Matthews interview, the Wentworth letter, and D&C 128.
This common practice is difficult to justify historically. Joseph explicitly helped to write the Cowdery letters, including Letter VII. He had them copied into his journal and gave explicit permission to others to reprint them.
By contrast, there is zero historical evidence that Joseph had anything to do with the anonymous Times and Seasons articles, and he never endorsed them explicitly or implicitly. The only link to him is the boilerplate at the end of the Times and Seasons listing Joseph as the editor, publisher and printer of the newspaper. To say this constitutes evidence that Joseph actually edited the paper would also constitute evidence that he physically printed the paper, a proposition no one takes seriously.
Based on historical evidence, Letter VII is much more Joseph's than the anonymous Times and Seasons articles. Plus, Letter VII is consistent with everything else Joseph said or wrote on the topic, while the anonymous Times and Seasons articles contradict everything else Joseph said or wrote on the topic.
Now, let's look at the list.
2 Feb 1833: American Revivalist
- The Book of Mormon is a record of the forefathers of our western tribes of Indians… By it, we learn that our western tribes of Indians, are descendants from that Joseph that was sold into Egypt, and that the land of America is a promised land unto them.
3 June 1834: (Zion's Camp) The story of Zelph
4 June 1834: (Zion's Camp) Joseph Smith believes that Illinois is the "plains of the Nephites" [Zion's Camp had crossed Ohio, Indiana, and Illinois to reach the banks of the Mississippi River, where Joseph wrote this letter. Emma was presumably familiar with the Book of Mormon, having served as a scribe for part of the translation and having been present during most of the translation.]
- The whole of our journey, in the midst of so large a company of social honest and sincere men, wandering over the plains of the Nephites, recounting occasionally the history of the Book of Mormon, roving over the mounds of that once beloved people of the Lord, picking up their skulls & their bones, as a proof of its divine authenticity, and gazing upon a country the fertility, the splendour and the goodness so indescribable, all serves to pass away time unnoticed.
November 1835: Journal account regarding Moroni's first visits
- He told me of a sacred record which was written on plates of gold, I saw in the vision the place where they were deposited, he said the indians were the literal descendants of Abraham he explained many
thingsof the prophesies to me
- [This account was not written by Joseph Smith. It originated as a conversation with Robert Matthews in 9-11 November 1835, recorded by Warren Parrish in Journal, 1835-1836 here. and by Warren Cowdery here. Joseph related the events to Matthews after Letter VII was published.]
July 19, 1840: Joseph teaches that the Land of Zion consists of North and South America
[This account was the first sermon recorded by 19-year-old Martha Jane Knowlton Coray. It is the subject of a separate blog post, but when read in context, Joseph most likely was referring to North and South America meaning North and South United States, not the continents. It has been misconstrued ever since.]...speaking of the Land of Zion, It consists of all N[orth] & S[outh] America but that any place where the Saints gather is Zion which every righteous man will build up for a place of safety for his children...The redemption of Zion is the redemption of all N[orth] & S[outh] America." (emphasis added)
16 November 1841: Joseph dictates the Bernhisel letter
- 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.
1 March 1842: Wentworth letter
- I was also informed concerning the aboriginal inhabitants of this country, and shown who they were, and from whence they came; a brief sketch of their origin, progress, civilization, laws, governments, of their righteousness and iniquity, and the blessings of God being finally withdrawn from them as a people was made known unto me: I was also told where there was deposited some plates on which were engraven an abridgement [abridgment] of the records of the ancient prophets that had existed on this continent....
- The principal nation of the second race fell in battle towards the close of the fourth century. The remnant are the Indians that now inhabit this country. This book also tells us that our Saviour [Savior] made his appearance upon this continent after his resurrection, that he planted the gospel here in all its fulness [fullness], and richness, and power, and blessing; that they had apostles, prophets, pastors, teachers and evangelists; the same order, the same priesthood, the same ordinances, gifts, powers, and blessing, as was enjoyed on the eastern continent, that the people were cut off in consequence of their transgressions…
- [An important part of this letter that people forget (or ignore) is that it was adapted from Orson Pratt's 1840 pamphlet "A[n] Interesting Account of Several Remarkable Visions." Pratt quoted from Letter VII, but he also spent several pages describing the Central/South American theory of geography. Joseph deleted all of that when he wrote the Wentworth letter, a clear repudiation of that geography theory. Instead, Joseph specified that the remnant of the Nephite/Lamanite nation are the Indians that inhabited the United States in 1842.]
15 July 1842: Joseph Smith discusses high civilization in the Americas, uses mound-builders and Guatemalan ruins as an example [That sentence is false. Nothing in this editorial states or implies Joseph wrote it. It is signed "Ed." for Editor; it is not signed by Joseph Smith. There is no evidence that Joseph wrote, edited, or even saw this article before or after it was published. He and Oliver Cowdery had unequivocally identified the location of the Hill Cumorah. Why Joseph let others speculate about the rest is the topic of a separate post, but he never varied from Letter VII.]
- If men, in their researches into the history of this country, in noticing the mounds, fortifications, statues, architecture, implements of war, of husbandry, and ornaments of silver, brass, &c.-were to examine the Book of Mormon, their conjectures would be removed, and their opinions altered; uncertainty and doubt would be changed into certainty and facts; and they would find that those things that they are anxiously prying into were matters of history, unfolded in that book. They would find their conjectures were more than realized-that a great and a mighty people had inhabited this continent-that the arts sciences and religion, had prevailed to a very great extent, and that there was as great and mighty cities on this continent as on the continent of Asia. Babylon, Ninevah, nor any of the ruins of the Levant could boast of more perfect sculpture, better architectural designs, and more imperishable ruins, than what are found on this continent. Stephens and Catherwood's researches in Central America abundantly testify of this thing. The stupendous ruins, the elegant sculpture, and the magnificence of the ruins of Guatamala [Guatemala], and other cities, corroborate this statement, and show that a great and mighty people-men of great minds, clear intellect, bright genius, and comprehensive designs inhabited this continent. Their ruins speak of their greatness; the Book of Mormen [Mormon] unfolds their history.-ED.
15 Sept. 1842: Speculation that Palenque is a Nephite city
Mr. Stephens' great developments of antiquities are made bare to the eyes of all the people by reading the history of the Nephites in the Book of Mormon. They lived about the narrow neck of land, which now embraces Central America, with all the cities that can be found. Read the destruction of cities at the crucifixion of Christ...Let us turn our subject, however, to the Book of Mormon, where these wonderful ruins of Palenque are among the mighty works of the Nephites:—and the mystery is solved...Mr. Stephens' great developments of antiquities are made bare to the eyes of all the people by reading the history of the Nephites in the Book of Mormon. They lived about the narrow neck of land, which now embraces Central America, with all the cities that can be found. Read the destruction of cities at the crucifixion of Christ, pages 459-60. Who could have dreamed that twelve years would have developed such incontrovertible testimony to the Book of Mormon? (emphasis added)<ref?John Taylor (editor), "Extract from Stephens' 'Incidents of Travel in Central America'," Times and Seasons 3 no. 22 (15 September 1842), 915. off-site GospeLink (requires subscrip.)
1 Oct. 1842: Zarahemla "stood upon this land" of Central America
[W]e have found another important fact relating to the truth of the Book of Mormon. Central America, or Guatimala [Guatemala], is situated north of the Isthmus of Darien and once embraced several hundred miles of territory from north to south.-The city of Zarahemla, burnt at the crucifixion of the Savior, and rebuilt afterwards, stood upon this land as will be seen from the following words in the book of Alma...It is certainly a good thing for the excellency and veracity, of the divine authenticity of the Book of Mormon, that the ruins of Zarahemla have been found where the Nephites left them: and that a large stone with engravings upon it as Mosiah said; and a 'large round stone, with the sides sculptured in hieroglyphics,' as Mr. Stephens has published, is also among the left remembrances of the, (to him,) lost and unknown. We are not going to declare positively that the ruins of Quirigua are those of Zarahemla, but when the land and the stones, and the books tell the story so plain, we are of opinion, that it would require more proof than the Jews could bring to prove the disciples stole the body of Jesus from the tomb, to prove that the ruins of the city in question, are not one of those referred to in the Book of Mormon...It will not be a bad plan to compare Mr. Stephens' ruined cities with those in the Book of Mormon: light cleaves to light, and facts are supported by facts.(emphasis added)
- Joseph Smith, “Mormonism,” The American Revivalist and Rochester Observer 7/6 (February 2, 1833). Only the last two paragraphs of Joseph’s letter to the newspaper were printed. The entire letter appeared eleven years later in the November 15, 1844 issue of the Times and Seasons.
- Dean C. Jessee, The Personal Writings of Joseph Smith, [original edition] (Salt Lake City, Utah: Deseret Book, 1984). ISBN 0877479747. GL direct link
- JS Journal, Nov 1835 
- Martha Jane Knowlton Coray, [edited by Dean C. Jessee], "Joseph Smith's July 19, 1840 Discourse," Brigham Young University Studies 19 no. 3 (Spring 1979), 392.
- Dean C. Jessee, The Personal Writings of Joseph Smith, revised edition, (Salt Lake City, Utah: Deseret Book, 2002), 533.
- Joseph Smith, "Church History," Times and Seasons 3 no. 9 (1 March 1842), 707. off-site GospeLink (requires subscrip.). See also History of the Church, 4:535–541. Volume 4 link
- Joseph Smith (editor), "American Antiquities," Times and Seasons 3 no. 18 (15 July 1842), 860. off-site GospeLink (requires subscrip.)
- Kenneth W. Godfrey, "What is the Significance of Zelph In The Study Of Book of Mormon Geography?," Journal of Book of Mormon Studies 8/2 (1999): 70–79. off-site wiki Godfrey believes that the author was either John Taylor or Wilford Woodruff.
- John E. Clark, "Archaeology, Relics, and Book of Mormon Belief," Journal of Book of Mormon Studies 14/2 (2005): 38–49. off-site wiki Clark believes that the author was Joseph Smith.