I guess I’d like to know if the natives in what is now the United States had any idea about the huge cities and structures further south. I doubt they would have, but on the other hand, if someone not from a city building culture would seen a huge freakin pyramid or a city with thousands and thousands of people, they probably would be telling stories about it around the campfire for a long time.
I don’t know the answer to the question, but I do know that first, the Mandan people in South Dakota spoke a language related to Aztec, and second, that Aztec trade goods have been found in the far north. If languages and trade goods were able to make it north, then so would stories of the cities.
While not as large Tenochtitlan, the Cahokia city state of the Mississippian culture (near St. Louis) boasted a population of 20,000 and built an earthen mound taller than the pyramids of the Aztecs. Cahokia was occupied for nearly 800 years.
Well, while not quite on the scale of the Inca/Maya/Aztec there were city-building meso-american countries in what is now the US. The “Pueblo” peoples of the American South West built cities such as Chaco canyon.
The book Guns, Germs, and Steel discusses this actually. According to the Jared Diamond (the author) one of the reason for the dominance of Eurasian culture is the geography of Asia and Europe means it is easier for culture, tehcnology, and ideas to spread from Asia to Europe and vice versa, where as the geography of America makes the same thing much harder (and also as the “axis” of America is north-south, the transfer of agricultural technology will be harder as the climate will be different).
Correction: not taller, but larger across the base.
I once visited a site in northern Mexico that was very close to the US border, just an hour’s drive or so south of New Mexico. I believe it was an Aztec site and considered an outpost. This was a long time ago; it may have been pre-Aztec. But certainly that would have been the farthest extent north. There was no pyramid there, but I do remember “an I-shaped ball court.” I cannot remember if that was a feature of the Aztecs or the people before them.
Just how old are you, sir?
As Chronos has noted, there’s evidence of trade and trade goods well into the present-day US. In addition, there are reconstructions of earthen structures along the Mississippi that suspiciously resemble the Aztec pyramids. I think the general culture made itself felt about halfway up the present US at least.
By the way, there’s a 1963 movie about conflict between tribes that lived in the present US and Mayans: Kings of the Sun. Directed by J. Lee Thompson (Guns of Navarone), it stars all-purpose ethnic Yul Brynner as Chief Black Eagle and George Chakiris as Mayan chief Balam, with a bunch of WASPS playing other indians. A very, very weird flick:
Pretty ancient. But I should have added that I did not visit the site in its heyday. It was some years afterward. 
Do you mean, “the territory of the present-day US,” or is this another benefit of NAFTA?
Sailboat
The Mississippian mound building culture had its own out-post here. Complete with pyramid shaped mounds. It was occupied around 1000 AD. This would be about as far north as an Aztec influence can be argued (rightly or wrongly)
When Coronado made his epic trip (looking for the Cities of Gold), he had aztek guides-these men were able to communicate with the local natives. Coronado got as far north as Kansas-and his guides were able to communicate.
So I would assume that there was some form of cummuncation, north of the Aztec empire.
My question: did the Azteks trace with the incas in Peru?
He was rather coy when mammoth hunting got mentioned in my thread about obsolete skills. I think he’s some kind of immortal.
Just curious: is there a reason to think that the Mandan moved north from proto-Aztecan-speaking land, rather than the reverse? I know the mythic Aztlan was north of Aztec territory, and as far as I understood all the Native American settlement was ultimately N > S [the odd trans-Pacific trade aside], so I’d think it would be more logical that the Mandan were distant kin who’d never moved far from the homeland rather than northward migrants from what-is-now Mexico.
Looking around online, wikipedia has a nice map of the northern chunk of the language family here.
You know, there’s this NYPD homicide detective he should meet.
IIRC, the Aztecs’ own mythology was that their people came from up around what we would now call Baja California, and moved southeast to found what eventually became Tenochtitlan. At their zenith, the Aztecs sent merchants and explorers all over Central America and lower North America, and it wouldn’t surprise me at all that nomadic Indians as far north as present-day Missouri and Wisconsin might have some vague, garbled awareness of the Aztec civilization.
For an excellent historical novel on the subject, I highly recommend Gary Jennings’s Aztec (although his characters never get north of the Rio Grande, IIRC).
Modesty prevents me from speaking. 
Dr. D’Amato?
The name’s Amsterdam.
There is a structure in one of the Anasazi sites that, according to some archaeologists, resembles a Meso-American ball court. This leads some to speculate that the Anasazi leaders may have been influenced by Aztec or Maya culture and religion. This interpretation is hotly contested, however. Very thin evidence, lots of room for speculation.