Fort Niagara, also known as Old Fort Niagara, is a fortification originally built by New France to protect its interests in North America, specifically control of access between the Niagara River and Lake Ontario, the easternmost of the Great Lakes. The fort is on the river's eastern bank at its mouth on Lake Ontario. Youngstown, New York, later developed nearby.

The Niagara River flows north from Lake Erie to Lake Ontario, forming part of the border between Ontario, Canada, to the west, and New York, United States, to the east. The origin of the river's name is debated. Iroquoian scholar Bruce Trigger suggests it is derived from a branch of the local Neutral Confederacy, referred to as the Niagagarega people on several late-17th-century French maps. George R. Stewart posits that it comes from an Iroquois town named Ongniaahra, meaning "point of land cut in two."