Waterloo is a municipality in Wallonia, located in the province of Walloon Brabant, Belgium, which in 2011 had a population of 29,706 and an ar…Waterloo is a municipality in Wallonia, located in the province of Walloon Brabant, Belgium, which in 2011 had a population of 29,706 and an area of 21.03 km. Waterloo lies a short distance south of Brussels and immediately south of the official language border between Flanders and Wallonia. Waterloo is most famous for being the site of the Battle of Waterloo in 1815, where the resurgent Napoleon was defeated for the final time.