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