The U.S. Census Bureau says the population in the United States will likely pass 300 million in the next week.
The Census Bureau maintains a population clock on its Web site, showing the U.S. population approaching the milestone.
Demographers say much of the U.S. population growth results from immigration and the children of immigrants. Last month, the Census Bureau said the Hispanic population, with nearly 43 million people, is the largest ethnic or race minority in the United States.
Immigration is a key issue in next month's Congressional elections, with deep divides on how to handle the illegal immigrants that enter the country, mainly through Mexico.
President Bush last week signed a law that provides more than $1 billion for fencing and enhanced security along the U.S. border with Mexico.
Both the outgoing and incoming presidents of Mexico criticized the plan for the fence, saying it will not solve the problem.