|The following is based on Van Buren and is not canon.|
New Jerusalem was a town built within the remaining ruins of Salt Lake City.
New Jerusalem's prophet and apostles repeatedly voted to have no commerce with outsiders from other, failed communities, refugees, or tribals. In 2233, a number of angry tribals, raiders, and disassociated attackers ganged up on New Jerusalem's defenders, sacked the settlement in the process, and killing most of the Mormons that did not flee, or attempted to flee.
According to the New Canaan design document, the new living prophet, Judah Black, led most of the surviving remnants of the Mormon community north to Ogden, Utah, where they established the town of New Canaan. The Burham Springs design document notes that Salt Lake City is unsuitable for the NCR outpost, as is Burham Springs, which is affected by a constant fire.
Behind the scenes
New Jerusalem is based on the real world location of Salt Lake City, the capital and most populous city of Utah.