Niagara is a city in Marinette County, Wisconsin, United States. The population was 1,880 at the 2000 census. The city lies to the north of and adjacent to the Town of Niagara.On July 31 2008 a gunman fatally shot three teenagers swimming in the Menominee River near Niagara. Scott J. Johnson of Kingsford, MI has been arrested, b...