The United States is the most populous country in the Americas and the Western Hemisphere, with a projected population of 342,034,432 on July 1, 2025, according to the U.S. Census Bureau. With about 4% of the world's population, it is the third most populous country. The U.S. population grew 2.6% between the 2020 federal census of 331,449,281 residents and the 2024 official annual estimate of 340,110,998. These figures include the 50 states and the federal capital, Washington, D.C., but exclude the 3.6 million residents of five unincorporated U.S. territories (Puerto Rico, Guam, the U.S. Virgin Islands, American Samoa, and the Northern Mariana Islands) as well as several minor uninhabited island possessions. The Census Bureau showed a population increase of 0.98% for the 12-month period ending in July 2024, slightly below the world estimated annual growth rate of 1.03%. By several metrics, including racial and ethnic background, religious affiliation, and percentage of rural and urban divide, the state of Illinois is the most representative of the larger demography of the United States.
The United States population almost quadrupled during the 20th century—at a growth rate of about 1.3% a year—from about 76 million in 1900 to 281 million in 2000. It is estimated to have reached the 200 million mark in 1967, and the 300 million mark on October 17, 2006. Foreign-born immigration caused the U.S. population to continue its rapid increase, with this population doubling from almost 20 million in 1990 to over 45 million in 2015, representing one-third of the population increase. The U.S. Census Bureau reported in late 2024 that recent immigration to the United States had more than offset the country's lower birth and fertility rates: "Net international migration’s influence on population trends has increased over the last few years. Since 2021, it accounted for the majority of the nation’s growth—a departure from the last two decades, when natural increase was the main factor." This in turn led to an increase in the U.S. population in each of the years 2022, 2023, and 2024 (+0.58%, +0.83%, and +0.98%, respectively).