It has not been easy to find the statistics, but DongTeam.org has finally found some figures on the Dong from the 2000 Census. Just like the United States and other countries, census figures have to be bought. Eventually, they trickle down to the common man, but the governments like a little return on the expense of such a wide sweeping venture.
DongTeam has posted some updated numbers on the general information page including total Dong populations from census figures of the last few decades and also populations of Dong in the three main Dong provinces. Prior to the new figures, DongTeam had projected three million Dong, and the total population is just shy of that number.