Numbers 1:45

“So were all those that were numbered of the children of Israel, etc.] Of all the tribes, excepting Levi, that is, all the sums of the number of the children of Israel; all put together made the sum total given in the next verse: by the house of their fathers, from twenty years old and upward, all that were able to go forth to war in Israel; all in every tribe, family, and house, that were above twenty years of age, healthful and strong, and fit for war.”

“all they that were numbered were six hundred thousand, &c.--What an astonishing increase from seventy-five persons who went down to Egypt about two hundred fifteen years before [see on Gen 46:8], and who were subjected to the greatest privations and hardships! And yet this enumeration was restricted to men from twenty years and upwards [Num 1:3]. Including women, children, and old men, together with the Levites, the whole population of Israel, on the ordinary principles of computation, amounted to about 2,400,000.”

“The enrollment, being taken principally for military purposes (compare Numbers 1:3, Numbers 1:20), would naturally be arranged by hundreds, fifties, etc. (cf. 2Ki 1:9, 2 Kings 1:11, 2 Kings 1:13). In eleven tribes the number enrolled consists of complete hundreds. The difference, in this respect, observable in the case of the tribe of Gad here Numbers 1:25, and of the tribe of Reuben at the later census Numbers 26:7, is probably to be accounted for by the pastoral, and consequently nomadic, habits of these tribes, which rendered it difficult to bring all their members together at once for a census. Judah already takes precedence of his brethren in point of numbers (compare Genesis 49:8…”