The study by UCLA researchers says California had 6.4 million uninsured residents before the downturn began in 2007. Now there are 8.4 million uninsured -- that's one fourth of the population under age 65.
The report blames high unemployment for loss of health benefits.
"Just about half of Californians get their coverage through employer-based coverage and so when the economy's tough and people lose their job, health coverage tends to go with it," says Anthony Wright from Health Access.
The study says the number of uninsured residents went up in every single county, but in the Bay Area, the rate was lower than the state average.