According to the LA Times the 2 counties contain more than half the nation's most heavily crowded neighborhoods, with rising rents far out outpacing incomes. From the outside looking in it's hard to tell, because places such as Maywood and Huntington Park don't look the highrise neighborhoods you see in Chicago or Boston. But behind the closed doors of bungalows or squat apartment buildings in overcrowded LA and Orange County neighborhoods are thousands more people per square mile.

"This is an example of poverty that can go unseen in our communities," says Jason Mandell, spokesman for United Way of Greater Los Angeles.

The overcrowding is caused in part because of rising rents, which have easily outpaced incomes across the region. A federal study 3 years ago found that between 1990 and 2009 rents in the LA metro area rose more than 20% while incomes of renters sagged 6% after adjusting for inflation. Experts say building is unusually difficult in LA, one of the factors that contributes to the affordable housing shortage.

Researchers at UCLA and University of North Carolina at Chapel Hill have found that children in overcrowded homes have poorer health, worse scores on math and reading tests and more behavioral and emotional problems such as depression and tantrums — even when poverty as a factor is taken into account. Read MORE in the LA Times.