The United States of America (USA), commonly known as the United States (U. S. or US) or America, is a country comprising 50 states, a federal district, five major self-governing territories, and various possessions. [i] At 3. 8 million square miles (9. 8 million km2), the United States is the world's third or fourth largest country by total area[d] and is slightly smaller than the entire continent of Europe. With a population of over 327 million people, the U. S. is the third most populous country. The capital is Washington, D. C. , and the most populous city is New York City. Most of the country is located contiguously in North America between Canada and Mexico.