President Joseph Fielding Smith wrote the following about the New Jerusalem:
“The prevailing notion in the world is that this [the New Jerusalem] is the city of Jerusalem, the ancient city of the Jews which in the day of regeneration will be renewed, but this is not the case. We read in the Book of Ether that the Lord revealed to him many of the same things which were seen by John. Ether, as members of the Church will know, was the last of the prophets among the Jaredites, and the Lord had revealed to him much concerning the history of the Jews and their city of Jerusalem which stood in the days of the ministry of our Savior. In his vision, in many respects similar to that given to John, Ether saw the old city of Jerusalem and also the new city which has not yet been built, and he wrote of them as follows as reported in the writings of Moroni:
[ Ether 13:2–11] …
“In the day of regeneration, when all things are made new, there will be three great cities that will be holy. One will be the Jerusalem of old which shall be rebuilt according to the prophecy of Ezekiel. One will be the city of Zion, or of Enoch, which was taken from the earth when Enoch was translated and which will be restored; and the city Zion, or New Jerusalem, which is to be built by the seed of Joseph on this the American continent.
[ Moses 7:62–64]
“After the close of the millennial reign we are informed that Satan, who was bound during the millennium, shall be loosed and go forth to deceive the nations. Then will come the end. The earth will die and be purified and receive its resurrection. During this cleansing period the City Zion, or New Jerusalem, will be taken from the earth; and when the earth is prepared for the celestial glory, the city will come down according to the prediction in the Book of Revelation.”
(Answers to Gospel Questions, 2:103–6).