There are three lands called “Land of Nephi”:
The first is where Nephi migrated and is called the Land of First Inheritance (not to be confused with the Jaredite Land of First Inheritance (Ether 7:16), or Lehi’s Land of First Inheritance—Ishmael:
Now the more idle part of the Lamanites lived in the wilderness and dwelt in tents and they were spread through the wilderness on the west in the land of Nephi yea, and also on the west of the land of Zarahemla in the borders by the seashore and on the west in the land of Nephi in the place of their fathers’ first inheritance, and thus bordering along by the seashore. (Alma 22:28)
Note: The “father” of the “Nephites” is “Nephi” and his “land of first inheritance” is different from Laman and Lemuel’s:
Now the Lamanites…were a wild and ferocious…believing…they were wronged in the wilderness…and again…while in the land of their first inheritance after they had crossed the sea (Mosiah 10:12-13)
And it came to pass that Ammon and Lamoni returned from the land of Middoni to the land of Ishmael which was the land of their inheritance. (Alma 21:18)
And Ammon went to the land of Ishmael the land being called after the sons of Ishmael who also became Lamanites. (Alma 17:19)
Now as Ammon was thus teaching the people of Lamoni continually we will return to the account of Aaron and his brethren for after he departed from the land of Middoni he was led by the Spirit to the land of Nephi even to the house of the king which was over all the land save it were the land of Ishmael and he was the father of Lamoni. (Alma 22:1)
And it came to pass that when the LAMANITES saw that they could not overpower the Nephites they returned again to their OWN LAND and many of them came over to dwell in the LAND OF ISHMAEL and the LAND OF NEPHI and did join themselves to the people of God who were the people of Anti-Nephi-Lehi. (Alma 25)
Zeniff…knowledge of the land of Nephi or of the land of our fathers’ first inheritance (Mosiah 9:1)
I will follow you even into your own land which is the land of our first inheritance…if ye seek to destroy us more we will seek to destroy you, yea, and we will seek our land the land of our first inheritance. (Alma 54:12-13)
2. City of Nephi / City of Lehi-Nephi
The second is the city Nephi built after fleeing from his brothers called the “City of Nephi”:
7 And we did take our tents and whatsoever things were possible for us and did journey in the wilderness for the space of many days and after we had journeyed for the space of many days we did pitch our tents.
8 And my people would that we should call the name of the place Nephi wherefore we did call it Nephi. (2 Nephi 5)
And now, it came to pass that after king Mosiah had had continual peace for the space of three years he was desirous to know concerning the people who went up to dwell in the land of Lehi-Nephi, or in the city of Lehi-Nephi; (Mosiah 7:1,2,4,21)
27 And now I would speak somewhat concerning a certain number who went up into the wilderness to return to the land of Nephi; for there was a large number who were desirous to possess the land of their inheritance.
28 Wherefore, they went up into the wilderness. And their leader being a strong and mighty man, and a stiffnecked man, wherefore he caused a contention among them; and they were all slain, save fifty, in the wilderness, and they returned again to the land of Zarahemla.
29 And it came to pass that they also took others to a considerable number, and took their journey again into the wilderness.
30 And I, Amaleki, had a brother, who also went with them; and I have not since known concerning them. And I am about to lie down in my grave; and these plates are full. And I make an end of my speaking. (Omni 1)
1 I, Zeniff, having been taught in all the language of the Nephites and having had a knowledge of the land of Nephi or of the land of our fathers’ first inheritance, and having been sent as a spy among the Lamanites that I might spy out their forces, that our army might come upon them and destroy them—but when I saw that which was good among them I was desirous that they should not be destroyed.
2 Therefore, I contended with my brethren in the wilderness, for I would that our ruler should make a treaty with them; but he being an austere and a blood-thirsty man commanded that I should be slain; but I was rescued by the shedding of much blood; for father fought against father, and brother against brother, until the greater number of our army was destroyed in the wilderness; and we returned, those of us that were spared, to the land of Zarahemla, to relate that tale to their wives and their children.
3 And yet, I being over-zealous to inherit the land of our fathers, collected as many as were desirous to go up to possess the land, and started again on our journey into the wilderness to go up to the land but we were smitten with famine and sore afflictions for we were slow to remember the Lord our God.
4 Nevertheless, after many days’ wandering in the wilderness we pitched our tents in the place where our brethren were slain, which was near to the land of our fathers. (200 BC)
5 And it came to pass that I went again with four of my men into the city, in unto the king, that I might know of the disposition of the king, and that I might know if I might go in with my people and possess the land in peace.
6 And I went in unto the king, and he covenanted with me that I might possess the land of Lehi-Nephi, and the land of Shilom. (Mosiah 9)
To clarify, a few verses later the Land of Lehi-Nephi is simply called the “Land of Nephi,” and the city, “City of Nephi”:
14 For in the thirteenth year of my reign in the land of Nephi, away on the south of the land of Shilom, when my people were watering and feeding their flocks, and tilling their lands, a numerous host of Lamanites came upon them and began to slay them, and to take off their flocks, and the corn of their fields.
15 Yea, and it came to pass that they fled, all that were not overtaken, even into the city of Nephi (i.e. Lehi-Nephi), and did call upon me for protection. (Mosiah 9)
3. Land of Nephi – Lamanite
The third is in reference to a larger, more generic land expression that included “Land of the Lamanites.”
Lamanites came down out of the land of Nephi (WoM 1:13)
go up to the land of Nephi that they might preach the things which they had heard and that they might impart the word of God to their brethren the Lamanites (Mosiah 28:1)
up to the land of Nephi to preach the word of God unto the Lamanites. (Alma 17:8)
the more idle part of the Lamanites lived in the wilderness…in the land of Nephi; (Alma 22:28)
Lamanites could have no more possessions only in the land of Nephi and the wilderness round about (Alma 22:34)
went up in the land of Nephi among the Lamanites (Alma 47;1)
drove all the Lamanites who were in the east wilderness into their own lands which were south of the land of Zarahemla (Alma 50:7)
fortifying the line between the Nephites and the Lamanites, between the land of Zarahemla and the land of Nephi, from the west sea running by the head of the river Sidon—the Nephites possessing all the land northward (Alma 50:11)
The Land of Nephi was the de facto Land of First Inheritance for Nephites, which was located along the West Sea and included elevated areas. It was south and west of the Land of Zarahemla, with a strip of wilderness between them and around them.