Grez-Doiceau is a municipality of Wallonia located in the Belgian province of Walloon Brabant. On January 1, 2006, Grez-Doiceau had a total population of 12,403. The total area is 55.44 km2 which gives a population density of 224 inhabitants per km2. Grez-Doiceau is watered by the Train, a tributary of the Dyle. The municipality consists of the following districts: Archennes, Biez, Bossut-Gottechain, Grez-Doiceau, and Nethen.