1 Chronicles 6

Chapter 6 gives the genealogies of Levi (3rd son of Jacob), who had three sons - Gershon, Kohath, and Merari.  The Levites were the only tribe in Israel that was not given a territory of land, but they rather received cities within each of the territories inherited by the other tribes.  This was not only the case because they were the priests of God, but Jacob had prophesied in Genesis 49:7 that Levi (and Simeon) would be divided in all of Israel.  This was fulfilled in how the Levites were spread throughout the tribes, and also because the tribe of Simeon ended up receiving land within the territory of Judah.