Fort Niagara post on the southern shore of Lake Ontario, at the mouth of the Niagara River, NW N.Y. It was strategically located on the water route to the fur lands. French explorer Robert LaSalle erected a blockhouse on the river in 1679; in 1726 a stone fort overlooking the river was completed. A British force, led by Sir William Johnson, captured Fort Niagara in 1759 during the French and Indian War (see under French and Indian Wars ). The British held the fort until 1796, when it was turned over to the United States by Jay's Treaty. During the War of 1812, the British captured Fort Niagara but returned it to the United States in 1815. The fort remained a U.S. military post until 1946. It is now a New York state park.