Judah

Judah as cited in the Book of Mormon is a reference to the southern kingdom of the Israelites. According to the Bible Dictionary of The Church of Jesus Christ of Latter-day Saints:

In the reign of Rehoboam the dominions of Solomon were broken up into two separate kingdoms, mainly in consequence of the jealousy between the tribes of Ephraim and Judah. The southern kingdom included the tribe of Judah and the greater part of Benjamin and had Jerusalem as its capital. On the whole it remained more faithful to the worship of Jehovah than the northern kingdom; it was less exposed to attack from the north and east, and the supreme power remained in the hands of the family of David until the Exile. It consequently managed to exist for 135 years after the downfall of the more populous and more powerful kingdom of Israel.[1]

The only references in the Book of Mormon of the kingdom of Judah that are not quotations from Isaiah are:

For it came to pass in the commencement of the first year of the reign of Zedekiah, king of Judah, (my father, Lehi, having dwelt at Jerusalem in all his days); and in that same year there came many prophets, prophesying unto the people that they must repent, or the great city Jerusalem must be destroyed.1 Nephi 1:4

And also a record of the Jews from the beginning, even down to the commencement of the reign of Zedekiah, king of Judah;1 Nephi 5:12

Behold, it came to pass that Mosiah discovered that the people of Zarahemla came out from Jerusalem at the time that Zedekiah, king of Judah, was carried away captive into Babylon.Omni 1:15