3 Nephi 5:12

And behold, I am called Mormon, being called after the land of Mormon, the land in the which Alma did establish the church among the people; yea, the first church which was established among them after their transgression.

I am called Mormon. I am named after the land of Mormon. That is where Alma started the church among the people. It was the first church started among them after they sinned.

My name is Mormon. I’m named after the land of Mormon, where Alma first established the church after the people had fallen away from God.