These are the people of Israel as listed by their fathers’ houses. All those listed in the camps by their companies were 603,550.
We have here the particular distribution of the twelve tribes into four squadrons, three tribes in a squadron, one of which was to lead the other two. Observe, 1. God himself appointed them their place, to prevent strife and envy among them.
Commenting on Numbers 2:3-34
These are those that were numbered of the children of Israel by the house of their fathers,.... As the number was taken by Moses and Aaron, assisted by twelve princes of the tribe, who were now constituted captains over them, as so many hosts or armies: all those that were numbered of the camp throughout their hosts: of the four camps, of Judah, Reuben, Ephraim...
These [are] those which were numbered of the children of Israel by the house of their fathers: all those that were numbered of the camps throughout their hosts [were] six hundred thousand and three thousand and five hundred and fifty. (h) Which were of twenty years and above.