what was the largest city in the Americas in 1114?

Cahokia, in modern-day Illinois and just east of St. Louis, would have been the largest city north of Mesoamerica in 1114. I have seen population estimates of up to 40K for the "metro area" (encompassing surrounding villages) and 20K for the main urban center. To give you an idea of just how large this was, European-founded cities in North America wouldn't surpass this level of population until just after the American Revolution. Cahokia would have been on par with or larger than almost any European city of the 12th century with the probable exceptions of Venice, Constantinople, and Paris.

As far as urban centers south of the Rio Grande, One of them would absolutely be the contender for largest city in the Americas, but I'm not 100% sure which would fit the bill in 1114. A candidate would certainly be Cholula, which is west of modern-day Puebla. I don't have a population estimate for 1114, but estimations at the time of the Spanish arrival 400 years later put the population at ~100,000, and this was after Cholula had been reduced in importance to a regional center by the rise of the Aztecs (this name is somewhat anachronous now, with the preferred term for the tribal alliance being Mexica, but I'm sticking with Aztec because it is familiar to most people) and their capital at Tenochtitlan (contemporary Mexico City). The Aztec capital had a population estimated at >200,000 when the Spaniards arrived in the early 16th century. Population estimates for their empire are educated guesswork, but I have seen anywhere from 5-10 million.

See these links/references:

Cholula:

http://www.famsi.org/research/pohl/sites/cholula.html

Cahokia

http://ngm.nationalgeographic.com/2011/01/cahokia/hodges-text

http://en.wikipedia.org/wiki/Cahokia