Silly is a Walloon municipality located in the Belgian province of Hainaut. On January 1, 2006 Silly had a total population of 7,995. The total area is which gives a population density of 118 inhabitants per km².
The name of the town derives from its stream, called the Sille (French) or Zulle (Dutch), and has no relation to the English word. In the Anglosphere, it has frequently been noted on lists of unusual place names.