Niagara County is in the U.S. state of New York.As of the 2020 census, the population was 212,666. The county seat is Lockport. The county name is from the Iroquois word Onguiaahra; meaning the strait or thunder of waters.. Niagara County is part of the Buffalo–Niagara Falls metropolitan area, and across the Canada–US border is the province of Ontario.. It is the location of Niagara Falls …