Say poverty in the Philadelphia area, and it conjures images of North Philadelphia or Kensington, not the suburbs.

But the suburbs on both sides of the Delaware River are becoming steadily poorer, part of a national trend that confounds long-held beliefs that life is always better in greener pastures beyond urban limits.

"People have this cliched notion of poverty being based in the inner city," said Adele LaTourette, director of the New Jersey Anti-Hunger Coalition, which has offices in Trenton and North Jersey. "But it's been moving into suburbia for some time.

"No one wants to think that their neighbors are becoming poor."

Across the United States, the population of poor Americans in the suburbs grew 64 percent from 2000 to 2010, twice the rate of urban poverty, according to a book being released Monday by the Brookings Institution. Confronting Suburban Poverty in America was written by Elizabeth Kneebone and Alan Berube at Brookings, a nonprofit public-policy think tank in Washington.

Each of Philadelphia's neighboring counties in Pennsylvania and South Jersey registered an increase in poverty between 2000 and 2010, Brookings research shows.

Still, the poverty rate in Philadelphia - the poorest of America's cities with populations of 1 million or more - remains three times higher than that of its suburbs. About 28 percent of Philadelphians are poor, compared to 8 percent of suburbanites.

The biggest change was in Camden County, where the poverty rate went up nearly 3 percentage points between 2000 and 2010, Brookings figures show. In Pennsylvania, the largest increase was in Delaware County, which went up nearly 2 percentage points during that same time.

The increasing number of poor in Philadelphia's suburbs means "the middle class, which traditionally moved to the suburbs over the last 40 years, has nowhere left to run to anymore as poverty becomes more of a suburban phenomenon," Berube, a senior fellow at Brookings, said in an interview.

Suburban poverty is hard to accept because it is less evident than poverty in Philadelphia.

"There's an invisibility," said Jan Leaf, executive director of the Lord's Pantry food bank in Downingtown, adding, "People pass all those restaurant parking lots out here that are packed with cars and have a hard time believing there are many people who don't know where their next meal is coming from."

In the Philadelphia area as elsewhere, the reasons for growth in suburban poverty are described by Brookings as the loss of jobs during the recession and its aftermath, the impact of foreclosures, and a growing population of lower-income immigrants moving to the suburbs.

"There are lots of people out here struggling right now," said Barbara Kummer, 58, a part-time home-health aide in Burlington Township.

Kummer lives with her 18-year-old daughter, who plans to start classes at Burlington County College in the fall - if there's enough money to attend.

Kummer, who is separated, makes around $10,000 a year. That is a far cry from the $27,000 salary she made at a high-tech company in the 1990s, where she worked as a quality-control inspector before being laid off.

Kummer receives $200 a month in food stamps, but she and her daughter still live below the federal poverty line of $15,510 for a family of two.

Like a lot of suburban poor, Kummer must spend a disproportionate share of her income on her car, a necessity in suburban communities. If Kummer's 2001 Nissan Altima fails, she has no way to get to work, she said. And that would be a disaster, she added.

Across the river in Darby, Betty Roy, 62, depends on relatives to drive her around.

For 30 years, she worked in retail stores, as well as in a laundry.

Now Roy, who is divorced, lives with her 14-year-old grandson, who has cerebral palsy. She survives below the poverty line on $140 in food stamps and on Social Security disability money resulting from a 2009 brain aneurysm that made work impossible.

"Sometimes, there's not enough food for us," said Roy, who frequents the Loaves and Fishes Food Pantry in Prospect Park, Delaware County. "I do without new clothes. I struggle."

For the suburbs to stop the slide into poverty, institutions dedicated to helping the urban poor need to look outside the cities, as well, Berube said.

"But it's a problem, because philanthropy continues to give to the inner city," he said.

That's because suburban poverty hits too close to home, LaTourette concluded. "Do you really want to think about your neighbor falling into that category? More of us are a paycheck from homelessness, but nobody wants to think about it."