Châtelet is a city and municipality of Wallonia located in the province of Hainaut, Belgium. It lies on the river Sambre. As of January 1, 2018, …Châtelet is a city and municipality of Wallonia located in the province of Hainaut, Belgium. It lies on the river Sambre. As of January 1, 2018, Châtelet had a total population of 36,101. The total area of the municipality is 27.03 km² which gives a population density of 1,336 inhabitants per km².