It is important to define the word "city" before beginning to answer how many there are. The United Nations has contradictory definitions in its reports. A report compiled from World Atlas calculated that there were 4,416 cities in the world with a population of over 150,000.
Some lists place Tokyo as the largest city in the world with a population of 37 million, but this is only when the municipality is counted as one city. The municipality also includes the city of Yokohama (population 3.6 million) and 86 other towns. The US Census Bureau estimated the 2013 population of New York as 8.4 million, the largest city in the US.