Albert Barnes Commentary Exodus 1:5

"And all the souls that came out of the loins of Jacob were seventy souls: and Joseph was in Egypt already." — Exodus 1:5 (ASV)

Seventy - See Genesis 46:27. The object of the writer in this introductory statement is to give a complete list of the heads of separate families at the time of their settlement in Egypt. See the note at Numbers 26:5.