For those who care - This is the top eleven most populated cities in the
4e Campaign Guide.
Waterdeep, Baldur's Gate and Luskan are not on the list, because their populations were not published. So assume Waterdeep and Baldur's Gate are the actual no 1. and no. 2.
1. Darromar in Tethyr (pop. 125,000
2. Athkatla in Amn (pop. 122,000)
3. Eltabbar in Thay (pop. 100,000)
4. Zazesspur in Tethyr (pop. 100,000)
5. Chavyondat in Estagrund (pop. 80,000)
6. Riatavin in Tethyr (pop. 80,000)
7. Alaghon in Turmish (pop. 75,000)
8. Veltalar in Aglarond (pop. 70,000)
9. Calimport in Calimshan (pop. 60,000)
10. Leuthilspar in Evermeet (pop. 60,000)
11. Selgaunt in Sembia (pop. 60,000)
I'm surprised they're as big as they are. Much bigger than european cities back in the day (so my sources tell me). Tethyr seems to win the Biggest Cities Award.