The Niagara Frontier refers to the stretch of land south of Lake Ontario and Lake Erie and extending westward to Cleveland, Ohio. The term dates to the War of 1812. This only includes the land east of the Niagara River and south of Lake Erie within the United States. The western side of the Niagara River on the Canadian/Ontario side is the Niagara Peninsula and is considered part of the Golden Horseshoe.

The Niagara Frontier is most commonly referred to as the land bordering the eastern Niagara River and southern shores of Lake Erie and Lake Ontario and is part of the region known as Western New York State. The Niagara Frontier also forms the eastern part of the Great Lakes North Coast, while its southeastern boundary forms what is known as ski country.

The National Weather Service office in Buffalo, New York currently defines the Niagara Frontier as the following:

Other, less common, definitions may also include the following areas: