The correct answer is - 40,000.
The estimates about the population of Cahokia by the archaeologists are that at max the city had around 40,000 people living in it. Cahokia is the most important site of the native American civilizations. It was next to the Mississippi River, and it represents the best of the Mississippian culture, and the North American civilizations (the Central American civilizations aside). The city is thought to have been settled by people from numerous tribes as it was prospering and that it become a mixture of multiple cultures and ethnicities over time. It reached its peak around the 13th century.