From Handy Answer: Native American Almanac
Cahokia in 1000 C.E. was the largest city in North America. Like Mesoamerican cities, the city featured pyramidlike mounds, wide plazas, and paved streets. Near present-day St. Louis, Cahokia centered on canals fed by the Missouri, Illinois, and Mississippi rivers. Trade items arrived by the tons in long canoes from the Great Lakes, the Gulf of Mexico, the Atlantic coast, Ontario, and Yellowstone. Founded around 750 C.E. and inhabited until 1350, Cahokia spread for five square miles, contained 120 temple mounds, and was home to 15,000 people. The city was related to thousands of smaller Mississippian mound centers that spread along river valleys from Lake Superior to the Mississippi Delta and from the western Appalachian valleys to the Oklahoma prairie.