The increase marked a sharp departure from homeless counts in 2011 and 2012, which showed the numbers of county residents without shelter dropping from 3% to 7% over previous years.
The biggest increases were among single men and people who have been without permanent shelter for a year or more. The study showed marked drops in homelessness among veterans and families.
The disappointing findings came despite more than $80 million in state, federal and local funds pouring into housing and other services last year through the Los Angeles Homeless Services Authority, a joint agency of the city and county that has overseen counts every two years since 2005.
It could get worse. More than $80 million in federal stimulus funds the county received for emergency housing since 2009 dried up in August, said Michael Arnold, the Homeless Services Authority's executive director.
According to the Los Angeles County Probation Dept., Gov. Jerry Brown's realignment program has diverted more than 15,000 low-level felons to Los Angeles County jails and probation programs. Arnold said that has resulted in thousands of people being released early into the community without adequate services or housing.
"The environment has conspired to make it look bad for Los Angeles," Arnold said. "We really need the economy to recover at a faster pace."
Homelessness tends to lag economic recovery, Arnold said, as people hit with job loss or other setbacks struggle to stay afloat then finally run out of options.
"It takes a long time to burn through your resources and become homeless," Arnold said.
At the same time, housing costs are rising with the improving economic outlook. Only 46% of California residents can afford to buy a home, and L.A. County rents are in the top 10 of any state, Arnold said.
In 2009, the average rent for a two-bedroom apartment in the Los Angeles-Long Beach area was $1,361. In 2013, that jumped to $1,421, according to a study by the National Low Income Housing Coalition.
The number of emergency shelters has dropped by 8%, also because of the downturn, officials said.
Homelessness among veterans dropped 23%, from 8,131 in 2011 to 6,291 in January 2013, when the new count was conducted. Family homelessness is down 28%. Arnold said that's a direct outgrowth of federal aid for veteran families.
A Los Angeles business task force on homelessness, in a statement, attributed the local rise to a spike in “hidden homeless” -- people who stay in garages or backyards who aren’t easily detected.
"Clearly this group needs further examination and attention from all those who are invested in ending homelessness," the task force said in a statement.
ALSO:Santa Monica police try to identify suspects in arson fire