Waterloo is a provincial electoral district in the province of Ontario that has been represented since 2018. The electoral district of Waterloo is defined to consist of the City of Waterloo plus that part of the City of Kitchener lying northerly of the CN Railway and northeasterly of the Conestoga Parkway. Based on 2016 census data, the population of the riding of Waterloo is 110,135
Between 1996 and 2018, the area currently defined as the provincial electoral district of Waterloo was part of the electoral district of Kitchener-Waterloo. Kitchener-Waterloo was defined to consist of the City of Waterloo and the part of the City of Kitchener that lies north of a line commencing at Wilmot Line and Highland Road West, then following to the intersection of Highland Road West and Fischer Hallman Road, turning northwest up Fischer Hallman Road and then tracing northeast along the CN railway located north of Shadeland Crescent following through to the easterly limit of Kitchener. The riding of Kitchener-Waterloo was dissolved prior to the provincial election in 2018.