Cahokia
Cahokia had about 1,000 people before circa 1050, its population grew rapidly after that date. According to a 2007 study "Between AD 1050 and 1100, Cahokia's population increased from between 1,400 and 2,800 people to between 10,200 and 15,300 people".  Archaeologists estimate the city's population at between 6,000 and 40,000 at its highest.