The Collaborative International Dictionary of English v.0.48:

Niagara \Niagara\, Niagara Falls \Niagara Falls\prop. n.
   A large waterfall on the Niagara River near Buffalo
   remarkable for the volume and constancy of the water flowing
   over it. That part of the waterfall in Canada is the
   Horseshoe Falls; the U. S. portion is called the American
   Falls.
   [WordNet 1.5] Niagara

WordNet (r) 3.0 (2006):

Niagara Falls
    n 1: waterfall in Canada is the Horseshoe Falls; in the United
         States it is the American Falls [syn: Niagara, Niagara
         Falls]
    2: a city in western New York State at the falls of the Niagara
       river; tourist attraction and honeymoon resort

U.S. Gazetteer Places (2000):

Niagara Falls, NY -- U.S. city in New York
   Population (2000):    55593
   Housing Units (2000): 27837
   Land area (2000):     14.053987 sq. miles (36.399657 sq. km)
   Water area (2000):    2.749057 sq. miles (7.120024 sq. km)
   Total area (2000):    16.803044 sq. miles (43.519681 sq. km)
   FIPS code:            51055
   Located within:       New York (NY), FIPS 36
   Location:             43.094305 N, 79.017339 W
   ZIP Codes (1990):     14301 14303 14304 14305
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Niagara Falls, NY
    Niagara Falls