If you've ever wondered how big the city of Tonawanda is, you're not alone. Tonawanda is one of the largest cities in Erie County, New York. As of the 2010 census, the city had a population of 15,130 people. Located on the northern edge of the county, Tonawanda is south of North Tonawanda and across the Erie Canal from Buffalo. Tonawanda is east of Grand Island and north of Buffalo and is part of the Buffalo-Niagara Falls metropolitan area.