The U.S. population is on target to hit 300 million this fall and it is a good bet the milestone baby — or immigrant — will be Hispanic.

No one will know for sure because the date and time will be just an estimate.

But both Latino immigrants and those born in the United States are driving the population growth, accounting for almost half the increase last year, more than any other ethnic or racial group.

White non-Hispanics, who make up about two-thirds of the population, accounted for less than one-fifth of the increase.

When the population reached 200 million in 1967, there was no accurate tally of U.S. Hispanics. The first effort to count Hispanics came in the 1970 census, and the results were dubious.

The Census Bureau counted about 9.6 million Latinos, a little less than 5 percent of the population, but the bureau acknowledged that figure was inflated.

In 1967, there were fewer than 10 million people in the U.S. who were born in other countries; that was not even one in 20.

Today, there are 36 million immigrants, about one in eight.

"We were much more of an insular society back then," said William Frey, a demographer at the Brookings Institution, a Washington think tank.

As of early Sunday, there were 299,058,932 people in the United States, according to the Census Bureau's population clock. The estimate is based on annual numbers for births, deaths and immigration, averaged throughout the year.

The 300 millionth person in the U.S. will likely be born — or cross the border — in October, though bureau officials are wary of committing to a particular month because of the subjective nature of the clock.