I recently read that Umbar was the most northerly haven where Black Numenoreans resided. Does that mean that most of them during the Third Age probably lived in Far Harad?
I know their numbers dwindled but I'm positive there were at least some left over.
There's very little about the Black Númenoreans in canon writings.
Firstly, the description of the Mouth of Sauron:
But it is told that he was a renegade, who came of the race of those that are named the Black Numenoreans; for they established their dwellings in Middle-earth during the years of Sauron's domination, and they worshiped him, being enamored of evil knowledge.
And secondly, in a footnote to the Appendices in Return of the King:
The great cape and land-locked firth of Umbar had been Númenorean land since days of old; but it was a stronghold of the King's Men, who were afterwards called the Black Númenoreans, corrupted by Sauron, and who hated above all the followers of Elendil.
That's it for Lord of the Rings; another reference is in the Akallabeth, where it is said:
But the King's Men sailed far away to the south; and the lordships and strongholds that they made have left many rumours in the legends of Men.
And there is also the following reference in Of the Rings of Power and the Third Age:
And Sauron gathered to him great strength of his servants out of the east and the south; and among them were not a few of the high race of Númenor. For in the days of the sojourn of Sauron in that land the hearts of well nigh all its people had been turned towards darkness.
So based on the texts, the only thing that can be said is "quite far".
