Key Points American cities are the economic drivers of the country, with some generating larger GDPs than entire states or foreign countries. Population: 4.02 million, comparable to Oklahoma (4.05 million) or Croatia (3.86 million). Population: 6.31 million, comparable to Missouri (6.2 million) or El Salvador (6.35 million). Population: 7.63 million, comparable to Arizona (7.43 million) or Laos (7.55 million). Population: 23.6 million, comparable to Florida (22.6 million) or Syria (24.7 million).