| Numbers 26:5New Century VersionThe tribe of Reuben, the first son born to Israel, was counted. From Hanoch came the Hanochite family group; from Pallu came the Palluite family group;See the chapter | 
Reuben was Israel’s first son. Reuben should have received the special privileges of the oldest son, but he had sexual relations with his father’s slave woman. So those special privileges were given to Joseph’s sons. (Joseph was a son of Israel.) In the family history Reuben’s name is not listed as the first son.