John Gill Commentary Numbers 26:19

"The sons of Judah: Er and Onan; and Er and Onan died in the land of Canaan." — Numbers 26:19 (ASV)

Ver. 19-22. And the sons of Judah were Er and Onan. And besides these he had Shelah, Pharez, and Zerah, from whom families sprang, but none from the two first: for Er and Onan died in the land of Canaan, where they were born; and that because of their sins, as the Targum of Jonathan adds, see Genesis 38:7–10.

So that there were but three families sprang from Judah, the Shelanites, Pharzites, and Zarhites; only the family of the Pharzites was divided into two families, the Hesronites and the Hamulites, so called from two sons of Pharez; the number of these families amounted to 76,500, so that there was an increase of 1900 since the last muster, which answers to Jacob's blessing, that he should be a praise among his brethren, (Genesis 49:8) .