Stormheim Vrykuls - around 5,000,000-6,000,000
Nightfallen Elves - around 8,000,000
Dalaran - around 10,000,000 including civilians, guards, troops, and heros.
Highmountain Drogbar Tribe - around 1,000,000-1,500,000
Tidemistress Athissa's Nagas - around 10,000,000
Burning Legion - around 20,000,000