Oswego (/ɒsˈwiːɡoʊ/ oss-WEE-goh) is a city in and the county seat of 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 (64 km) northwest of Syracuse and 74 miles (119 km) east-northeast of Rochester by road. The city promotes itself as "The Port City of Central New York".

The first European settlement at Oswego was a British trading post established in 1722, and it was first incorporated as a village in 1828 before becoming a city in 1848. British forces briefly captured the city during the War of 1812, but were defeated nearby later that same month. The canalization of the Oswego River was a major boon to Oswego, attracting settlement and investment; this was later bolstered by its status as a rail hub for much of the 19th and 20th centuries, though this status had begun to decline by the 1940s. During World War II, Fort Ontario was the site of the only Jewish refugee camp in the United States. Today, the city's economy is primarily based around manufacturing and services.

Oswego is governed by a mayor, currently Republican Rob Corradino, and a city council. The city is located within the Syracuse metropolitan area, and is also inside Syracuse's broader media market. It is bordered by the towns of Oswego, Minetto, and Scriba to the west, south, and east, respectively; and by Lake Ontario to the north. Oswego Speedway is a nationally known automobile racing facility. The State University of New York at Oswego (SUNY Oswego) is located just outside the city in the town of Oswego, on the shores of Lake Ontario, and is a major force in the area.

The British established a trading post in the area in 1722 and fortified it with a log palisade later called Fort Oswego, named after the native Iroquois place name "os-we-go" meaning "pouring out place". The first fortification on the site of the current Fort Ontario was built by the British in 1755 and called the "Fort of the Six Nations".

Fort Ontario was destroyed by the French upon capturing it in the Battle of Fort Ontario, during the French and Indian War. Construction of a second British fort began on the same site in 1759, but Fort Ontario was only used as a cannon emplacement. During the American Revolution, the British abandoned the Fort, and in 1778, American troops destroyed it. In 1782, the British reoccupied Fort Ontario, and didn't forfeit it to the U.S. until 1796, thirteen years after the cessation of hostilities in the Revolution.

During the War of 1812, a weaker American garrison at Fort Ontario was overwhelmed by superior British forces in order to stem the flow of supplies from the interior of New York state, but were later defeated near Oswego later that month. Throughout the 19th Century, the U.S. military maintained a presence at Fort Ontario.

Oswego was incorporated as a village on March 14, 1828, and the Oswego Canal, a branch of the Erie Canal, reached the area in 1829. The city was incorporated in 1848. When the city incorporated, its area and population were removed from the figures reported for the towns.

In the 1850s, at the height of a popular water-cure movement occurring in the United States, in turn stimulating growth, Oswego was the home of the Oswego Water Cure establishment, which Stonewall Jackson reportedly visited in August 1850.