It's funny how many of the Indian users on this thread are openly anti-muslim, anti-Bangladesh, anti-Bengali and yet claim to give an "educated" "true" idea about the population of Assam. What is more, it is often users from Gujarat, or North India and elsewhere being brainwashed by their media cominghere spouting their rubbish and claiming its true.
There are illegal Bangladeshi migrants in India, just as there illegal Bihari Indian migrants in Bangladesh. The numbers for either can't exceed half a million apiece. The number these racist nazi Hindutva killers are giving are just the population of the muslims in the region. When if they simply use their brain and look at the 1951 census there are millions of muslims in the Northeast even then, so after 60 years of population growth (and it will be high for muslims, as the government won't educate them and so it leads to many children), it will be several million.
These Bengali Muslims are as much native as anyone else is. What is more, their numbers are lower than they should be, I am from Sylhet and I know of loads of people in BD who are actually from Silchar and other places who had to flee from the Indian and Assamese genocide. My teacher is from Rangpur and she knows of loads of people in her area who fled from Guwahati and Goalpara into here area.
The problem with Bengalis is they didn't unite earlier. The Barak Valley Sylhetis stood up early enough to affirm they are Bengali ( a dialect of it). But the Goalpariya Bengalis didn't stand up and so they should. In addition, Assamese speaking Muslims are few and far between, what those people actually are is Bengali muslims from the region (Kamrup, Nagaon, Sonitpur) whop have been forced to say they're Assamese in the 1940s. If you look at the 1931 to 1951 decline of Bengali speaking population, you can see "Assam" or as I like to call it: Kamarupa is actually the home of Bengalis, Bodos, Assamese and other smaller groups. But Assamese have been claiming the whole thing for decades and Bodos have joined the fray with an anti-Muslim angle.
There needs to be an independent Kamarupa (including the Indic parts of Burma, North Arakan and Chin State) where the groups can live peacefully, this ethnic cleansing that is being carried out can't continue.