These ethnic families, which are of unequal size, are concentrated mainly in the mountainous provinces in the north. The Tay-Thai, numbering a little over 3 million (4.8% of the population), is the country’s second largest ethno-linguistic family. The Tay are concentrated in the North, especially in Cao Bang and Lang Son provinces where they represent between 77-80% of the population. The Thai, on the other hand, are mainly concentrated in Lai Chau and Son La, where they account from between 40-55% of the population. The Tay-Thai in the Northern Mountains represent 25-40% of the population. The Tay-Thai population has increased substantially in the settled parts of the northern uplands, except in the areas dominated by the Tay, as well in the provinces surrounding the delta. More recently, there has also been a significant growth in the Thai population on the plateaus and in Dong Nai, where communities of 19,000 to 33,000 inhabitants are now found.
The other two group are very much in the minority; the Hmong-Dao represent only 1.4% of the population and the Tibetan-Burmese community numbers only 29,000. These groups are concentrated in the three mountainous provinces of the North- Ha Tuyen, Hoang Lien Son, and Lai Chau—where diversified crops, and especially opium, are produced on the limestone plateaus. The Hmong-Dao account for 24-43% of the population of these provinces; their number is also increasing in the southern provinces bordering the Middle Region.