The King-Crane Commission report of 1919 detailed an estimate of the population of different areas of what they called "Occupied Enemy Territory Administration" of Levantine lands occupied by allies after World War I.
It includes a curious table showing the estimated population of each district of the OETA.
OETA East is roughly what became Transjordan.
OETA South | OETA West | OETA East | Totals | |
Muslims | 515,000 | 600,000 | 1,250,000 | 2,365,000 |
Christians | 62,500 | 400,000 | 125,000 | 587,500 |
Druses | 60,000 | 80,000 | 140,000 | |
Jews | 65,000 | 15,000 | 30,000 | 110,000 |
Others | 5,000 | 20,000 | 20,000 | 45,000 |
Totals | 647,500 | 1,095,000 | 1,505,000 | |
Grand Total | 3,247,500 |
So what became of these 30,000 Jews?
I can find no record of any significant Jewish population in Transjordan. My guess is that these estimates were not grounded in any real censuses or research. Because if the British had expelled 30,000 Jews from Transjordan, I think there were be some records of it!
Another piece of evidence that these 30,000 Jews never really existed comes from the Palestine Bulletin, May 9. 1930, with a very interesting anecdote:
If a significant Jewish community of 30,000 were already there, they would have been mentioned.
Of course, the Zionist Jews had little interest in settling in Transjordan as a trade for settling in Eretz Yisrael. (Revisionist Zionists, of course, wanted land on both sides of the Jordan.)
(h/t Irene)
UPDATE: Here is the original Doar Hayom article (h/t Yoel):