The United States Census Bureau provides this information on its website. As of June 2015, the U.S. population is over 321 million. In July 2014, the U.S. population was 318,881,992, and the most populated state was California with more than 38.8 million people.
The U.S. Census Bureau site has a population clock that gives other useful information, such as the world population and a list of the most populated countries. As of June 2015, the world population is more than 7.2 billion. The country with the most population is China with more than 1.38 billion people. With a population more than 1.25 billion, India is the second-most populated country.
This government website also provides information on the rate of worldwide births and deaths that occur, such as there is a birth every 8 seconds and a death every 13 seconds.