The Census Bureau said in a statement that the figure represents an increase of about 11.35 million people, or 3.67 percent, since the last population count on April 1, 2010.
"In January 2015, the U.S. is expected to experience a birth every eight seconds and one death every 12 seconds. Meanwhile, net international migration is expected to add one person to the U.S. population every 33 seconds," the Census Bureau said.
It said the combination of births, deaths and net international migration would add at least one person to the U.S. population every 16 seconds.
The Census Bureau projected the world population on Jan. 1 at about 7.21 billion, a 1.08 percent increase from New Year's day in 2014. It estimated that about 4.3 births and 1.8 deaths will occur worldwide every second in January.