THERE are now more young adults than there are baby boomers.

From 1947 through 2010, the largest single age group in the United States was born sometime in the 18 years after the end of World War II. In 1947, that was zero years old — babies who had not yet celebrated their first birthday. In 2010, it was 50-year-olds.

But the Census Bureau now estimates that the biggest such group last year was 22-year-olds. The largest of the baby boom contingents, people who were 53 last year, had fallen to fourth place. The second- and third-ranked age levels were 23- and 21-year-olds.

By one measure — the civilian population — baby boomers lost their status only late last year, according to the Census Bureau. But using a broader measure, which includes members of the armed forces who are stationed in the United States, the change took place in 2011.