The United States of America (USA), commonly known as the United States (U. S. or US), the States or simply America, is a country comprising 50 states, a federal district, five major self-governing territories, and various possessions. [h] At 3. 8 million square miles (9. 8 million km2), it is the world's third or fourth-largest country by total area[c] and is slightly smaller than the entire continent of Europe. Most of the country is located in central North America between Canada and Mexico. With an estimated population of over 328 million, the U. S. is the third most populous country. The capital is Washington, D. C. , and the most populous city is New York City.