Oswego (ŏswēˈgō) [key], city (1990 pop. 19,195), seat of Oswego co., N central N.Y., on Lake Ontario and the Oswego River; founded 1722, inc. as a city 1848. The largest U.S. port on Lake Ontario, it is a port of entry and a northern terminus of the New York State Canal System. The city's manufactures include steel and rolled aluminum. A trading post established there after the English founded Oswego (1722) became a vital outlet for the Albany fur trade. The strategic location prompted the building of Fort Oswego (1727), Fort George (1755), and Fort Ontario (1755; an active U.S. army post until 1946, now a state historic site). These fortifications were much contested in the colonial wars. The city's importance as a lake port came with the completion of the canal system (1918) and the St. Lawrence Seaway (1959). It is the seat of State Univ. College of Arts and Sciences at Oswego. Three nuclear power plants are northeast of the city. James Fenimore Cooper's novel The Pathfinder is set in the Oswego River valley.