moria

[Phrim]

I don't think Tolkien really gives a number anywhere. However, he does say this:

The power of Moria endured throughout the Dark Years and the dominion of Sauron, for though Eregion was destroyed and the gates of Moria were shut, the halls of Khazad-dûm were too deep and strong and filled with a people too numerous and valiant for Sauron to conquer from without.

If Moria could withstand the forces of Sauron at the height of his power, and by strength of numbers at that, it must have been greatly populated indeed.