The United States of America, commonly known as the United States or America, is a country consisting of 50 states, a federal district, five major self-governing territories, and various possessions.[g] At 3.8 million square miles (9.8 million km2), it is the world's third- or fourth-largest country by total area.[c] Most of the country is located in central North America between the countries of Canada and Mexico. With an estimated population of over 328 million, the U.S. is the third most popu