23 hours ago · St. Catharines is the most populous city in Canada's Niagara Region, the eighth largest urban area in the province of Ontario.As of 2017, St. Catharines has an area of 96.13 square kilometres (37.12 sq mi) and 140,370 residents. It lies in Southern Ontario, 51 kilometres (32 mi) south of Toronto across Lake Ontario, and is 19 kilometres (12 mi) inland from the …