Tonawanda is a city in Erie County, New York, United States. The population was 15,129 at the 2020 census. It is at the northern edge of Erie County, south across the Erie Canal from North Tonawanda, east of Grand Island, and north of Buffalo. It is part of the Buffalo-Niagara Falls metropolitan area.

Erie County is a county along the shore of Lake Erie in western New York State. As of the 2020 census, the population was 954,236. The county seat is Buffalo, which makes up about 28% of the county's population. Both the county and Lake Erie were named for the regional Iroquoian language-speaking Erie tribe of Native Americans, who lived in the area before 1654. They were later pushed out by the more powerful Iroquoian nations tribes. The county is part of the Western New York region of the state.