Boussu is a municipality of Wallonia located in the province of Hainaut, Belgium. As of January 1, 2006, Boussu had a population of 20,058. …Boussu is a municipality of Wallonia located in the province of Hainaut, Belgium. As of January 1, 2006, Boussu had a population of 20,058. The total area is 20.01 km², which gives a population density of 1,002 inhabitants per km².