And so Jacob, whose name God had changed to Israel, entered Egypt. All of the Israelites that existed in the world at the time were in that small group. They would remain there for 430 years (Exodus 12:40-41) until the Exodus.
Despite their eventual hardships, the Israelites had large families and grew very numerous:
Although there is no record of the precise number that left Egypt in the Exodus, a military census taken not long after listed the number of men 20 years of age and older who could serve in the army as 603,550 (Exodus 38:26). From that number, the total Israelite population of that time has been estimated at approximately 2 to 3 million.
How can a small group become a nation of millions in just over 4 centuries? A simple bit of arithmetic shows that it was easily possible. If the average Israelite family consisted of 4 children by the time the parents were 27 years old (the Bible record shows that families then were actually much larger), that would provide for a doubling of the population every 27 years (2 children to replace the parents, and 2 children to account for population growth). 430 years divided by 27 years is about 15 generations during the time Israel was in Egypt.
Beginning with the original 70 people, growth of the Israelite nation using our factors above would have been:
The example is of course a rough estimate, but it does prove the point that the Israelites could easily have increased to a great number in the given time.
Fact Finder: What route did the Israelites take during their time in the wilderness?
See Wilderness Journey