Highest population a US with these borders could achieve?

[Max Sinister]

Vive L'Empereur du Louisianne?

The thing was, French Louisiana was underpopulated. That's why it's so hard to imagine that TTL *Americans would sit in their little quarter and ignore the rest.

 

[TimTurner]

Those lands OTL have 145 million people. 200-220 is pretty feasible if fewer people go west of the Mississippi and you don't have a civil war.

Imagine how packed the Eastern Seaboard will be...

 

[NAF]

With so many more people being concentrated on the east coast, how much more populated could NYC be than in OTL?

 

[Arkenfolm]

Imagine how packed the Eastern Seaboard will be...

With so many more people being concentrated on the east coast, how much more populated could NYC be than in OTL?

I think you'd see more in the Midwest and even see North Carolina and Tennessee developing earlier (no Civil War and slavery ending by the 1860s, etc.) than see the East Coast being too crowded.

One area I'd expect to be much more populous and prosperous is border cities like Memphis or East St. Louis. The latter in particular would anchor a major transnational metropolitan area (and no doubt have a much much much more positive reputation). This would draw people away from the coasts.