The population of the 13 colonies was not static. It changed over the nearly one hundred and seventy years of the colonies's history. At the start of the American Revolution, the 13 colonies had their largest population of a combined 2.4 million.
However, the population was much smaller during the 1600s when European colonization in the region began. In 1640, there were just under 25,000 colonists. However, Pennsylvania, New Jersey, North Carolina, South Carolina, Georgia, and Delaware had not yet been established. By 1740, all 13 Colonies had been settled by Europeans. In that year there were just over 906,000 colonists in all thirteen of the colonies. It should be noted that Virginia was always the most populous colony.
You should also keep in mind that when the American Revolution began, nearly twenty percent of the total population of the 13 colonies consisted of enslaved Africans or slaves of African descent. Furthermore, the numbers above do not include the Native American population, of which no definitive census exists.