Oswego is a city in Oswego County, New York, United States. The population was 16,921 at the 2020 census. Oswego is situated at the mouth of the Oswego River on the southeastern shore of Lake Ontario in Upstate New York, about 40 miles northwest of Syracuse and 74 miles east-northeast of Rochester by road. The city promotes itself as "The Port City of Central New York." It is the county seat of Oswego County.