Albert Barnes Commentary Numbers 26:5

"Reuben, the first-born of Israel; the sons of Reuben: [of] Hanoch, the family of the Hanochites; of Pallu, the family of the Palluites;" — Numbers 26:5 (ASV)

The tribes are mentioned in the same order as in the earlier census (Numbers 1), except that Manasseh here precedes Ephraim, probably because it was now the larger tribe.

Seven of the tribes, three of which belong to the camp of Judah, show an increase in numbers; and five, among whom are the three belonging to the camp of Reuben, show a decrease. The greatest increase of any one tribe is in Manasseh. The most remarkable decrease is in Simeon, which now shows less than half its former strength.

Zimri, the chief offender in the recent transgression, belonged to this tribe (Numbers 25:14). His tribesmen probably had generally followed his example and, accordingly, had suffered most severely in the plague. In the parting blessing of Moses, uttered shortly after this date, the tribe of Simeon alone is omitted.

The families of all the tribes, excluding the Levites, number 57. The ancestral heads after whom these families are named correspond closely with the grandchildren and great-grandchildren of Jacob, listed in Genesis 46:8 and following. Both lists consist mainly of Jacob’s grandchildren; both also contain the same two grandchildren of Judah and the same two grandchildren of Asher.

The document in Genesis should be regarded as a list—not of those who personally went down with Jacob into Egypt, but rather of those whose names were transmitted to their descendants at the time of the Exodus as the heads of Israelite houses, and who may thus be considered the early ancestors of the people.