Barely half of adults are now part of the middle class, defined as a household making between $42,000 and $126,000 annually.

Richard Fry, who co-authored a new Pew research study, says that as the middle class has hollowed out, the upper income bracket has grown from 14 to 21 percent of Americans. That "upper class" now takes home nearly half of all annual income in the United States -- 49 percent, up from 29 percent in 1970.

"It's not that the middle Americans are worse off, it's that they're falling behind relative to upper income adults," Fry explained.

The lower income cohort has also increased from 16 to 20 percent since 1971.

Meredith Reilly, a 37-year-old social worker in New Jersey, used to think of herself as middle class. "It was the good life. It was wonderful. And now if I don't go to work, I don't get paid."

Her county job, which paid about $50,000 a year, was eliminated in the recession. A single mother of two, Reilly now works three part-time jobs and makes less money.

"I think the toughest part is not preparing a future for my children that my parents prepared for me."

"I just don't feel like the jobs are out there that are gonna put me back to where I was," said Reilly.