A new report says that the number of Americans living in neighborhoods with extreme poverty grew markedly in the last decade, erasing gains the U.S. made in eradicating poverty in the 1990s.

The Washington-based Brookings Institution research group said Thursday that at least 2.2 million more people now live in communities where at least 40 percent of the residents are poor. That is about a third more than the nearly 7 million people living in concentrated poverty in 2000. The U.S. defines poverty as a family of four living off an annual income of $22,300 or less.

The nation's worst economic downturn in 70 years left millions of people out of work, and often forced them out of their homes when they could no longer pay their mortgages. The report's author, Elizabeth Kneebone, said that with falling household income, the “2000s took an economic toll.”

Brookings said the midwestern and southern portions of the country were hardest hit, with lost manufacturing jobs and a large number of houses taken over by banks in loan foreclosures.

Recent government reports have also shown the effects of the recession from which the U.S. is still struggling to recover. U.S. household income dropped last year to its lowest level in a decade, while poverty rose to a 17-year high. Nearly 46 million Americans, a new record, now receive government assistance to help them buy food.