I have a region called Simcityland, and in it there are 16m people. Most of it's just forest and mountains and rivers, though; the population is crowded in an area I call the west coast mostly. On the opposite side of the map is Sydney, my largest city yet. It's probably 80% land, but it has about 1.2 million people.
My largest before that was Victoria, with 1.1 million, but I lost it due to computer issues.