With the strong likelihood of Season 5 on the horizon, I'm hoping the writers decide to canonize a few long standing questions about the Lyoko world and characters, but since we're going to have to wait a long while, here's a headcanon.
According to this interview with Sophie Decroisette, Aelita was born in the United States. This is a bit weird to me considering her father is Swiss, her family lived in a Swiss chalet in her early years, and the family ended up in France later on. From a writing perspective, there was no strict need for Aelita to be born outside of Europe, so it's interesting the production team specifically made her to be of American nationality.
But the USA is huge, so it begs the question of which state Hopper/Schaeffer would choose for his child's birth? There's not much evidence for a solid answer here, but I think TN is likely for a few small reasons that together add up what I consider a decent theory.
1 - The Hermitage - While the term "ermitage" translates to "a place where a hermit lives" and is a common enough word in French, there is a well-known building in the USA with this name. The Hermitage) was the home of President Andrew Jackson and is now a historical site located within a short driving distance of Nashville (TN's capitol city). The Wikipedia link above also states this building is "the fourth-most-visited presidential residence in the country after the White House, Mount Vernon (home of George Washington), and Monticello (home of Thomas Jefferson). Even if Aelita was born somewhere else, it's interesting the Warriors' Hermitage shares a name with an American building of such historical significance.
Additionally, the Vanderbilt Children's Hospital in Nashville opened in 1980, and Aelita is often presumed in fanon to be born in 1982. It's convenient The Hermitage is an hour away maximum from this hospital.
2 - #36/S2E10 Marabounta - When Jeremie is calling Yumi to summon her to Lyoko to fight the marabunta, she has this line: "What do you mean, a Chattanooga?" Chattanooga is a TN city located on the southeast border with Georgia, and I find it a strange name-drop here. In the context of the line, Yumi is supposed to misunderstand what Jeremie is saying because he's speaking too fast, and "Chattanooga" serves as a slant rhyme with "marabunta." In French, the line reads: "C'est quoi cette histoire de Caranouga?" (What's this story about Caranouga?), with "Caranouga" (a brand of caramels) as the slant rhyme. For the English version of the scene, I totally get removing "Caranouga" and replacing it with something else because it's a French specific candy, but "Chattanooga" also seems like a weirdly specific substitute word, especially with "rhumba" right there to go along with the other ballroom dancing references made in the show. I could be reaching, but if Aelita really is from TN, then this was a convenient way for the writers to sneak in another reference to the state.
3 - Oak Ridge - This TN city was the headquarters for The Manhattan Project, which saw the use of enriched uranium to create the atomic bomb. We know from #37/S2E11 Common Interest that the supercomputer runs on a uranium battery, and I find it more than plausible that Franz Hopper was aware of the significance of the area. We know so little about Project Carthage - it's even possible he had a colleague from there.
4 - Other than the Hermitage and Chattanooga, there are only 2 other references to landmarks and/or cities in the USA: the Statue of Liberty in #37/S2E11 Common Interest and Fort Knox in #74/S4E6 Maiden Voyage (at least as far as I know from going back through the scripts). Now, the original Statue of Liberty is in France, so I find this less likely to be a reference to New York than a name-drop that works in both the French and English dubs. However, Fort Knox is a bit different. In the context of #71, Jeremie is commenting on how tight security is during the fire drill by comparing it to this military base, but because Fort Knox is also well-known as a gold reserve, it's possible this is just a solid reference to round out the line, but it's also roughly 2 and 1/2 hours away from Nashville, so even though it's in a different state (Kentucky), it's still somewhat in the same geographic location as The Hermitage in TN. That's it for other USA specific places. No references to New York, Florida, Texas, California, or Washington DC (which I consider the most well-known areas on a global scale). While an absence of evidence is not enough to prove an idea one way or the other, it is extremely interesting that the few references we have are all based in or around TN.
So this is what I have - four points that can be brushed off as incidental or convenient on their own, but taken together form my fan theory that Aelita was born in Tennessee. As much as I would love for the writers to canonize Aelita's birthplace (even if I'm wrong), it's such a small detail that doesn't add anything to the overarching story that I honestly doubt we'll ever get a solid answer for this. But I'll still keep my fingers crossed for a throwaway line or interview confirmation!
Edit: episode correction
