The 300 millionth American is expected to arrive this week, but unlike past population milestones, there's a good chance that landmark resident won't necessarily be a newborn.

She or he may be an adult immigrant.

All the U.S. Census Bureau knows for sure is that a baby is born in the country every 7 seconds, a new immigrant arrives every 31 seconds on average and someone dies every 13 seconds, for a net average gain of one resident every 11 seconds.

A lot has changed since 1967, the year that America hit the 200 million mark. At that point, foreign-born residents made up just 5 percent of the population. By 2004, with the advent of legal reforms in 1965 that revived immigration, that figure had jumped to 12 percent.

Put another way, immigrants and their children and grandchildren have accounted for more than half of the population increase in the United States since 1967, according to the Pew Hispanic Center.

"We are returning to our melting-pot roots," said William Frey, a demographer for the Brookings Institution.

Immigrants accounted for 15 percent of Americans in 1915, when the nation's population hit 100 million. The largest group was Germans, and rising anti-immigration sentiment led Congress to adopt immigration controls in the 1920s and 1930s.

Today's fights about immigrants, especially those here illegally, don't compare with the intense fear and hatred at the dawn of the 20th century, said Mike Hout, a sociology professor at the University of California at Berkeley.

"Look at Columbus Day in 1900, when the first really big parade was organized in New York," Hout said. "Two days prior, the state Assembly passed a bill prohibiting hiring alien Italians for state contracts. The New York Times quoted a socialite saying she was employing Italian gardeners, but she'd fire them as her patriotic duty.

"For the march, 30,000 Italians and Italian Americans congregated ... and two blocks later they were greeted with a shower of bricks from Irish workers on a local construction site protesting Italians taking their jobs. Cops broke up the march with billy clubs."