Amsterdam is a city in Montgomery County, New York, United States. As of the 2010 census, the city had a population of 18,620. The name is derived from the city of Amsterdam in the Netherlands.The city of Amsterdam is surrounded on the north, east, and west sides by the town of Amsterdam. The city developed on both sides of the Mohawk River, with the majority located on the north bank. The Port Jackson area on the south side is also part of the city.