The census, which began Tuesday night, will take three days to complete.
To qualify for federal funding to assist the homeless, the U.S. Housing and Urban Development Department requires communities to count their homeless populations on a given day every two years. Similar efforts are taking place nationwide this week. Federal housing officials define the homeless as people living in emergency shelters and transitional housing, or in places not fit for human habitation such as sidewalks, cars, parks and abandoned buildings.
The L.A. city-county count, which covers about 4,000 square miles, is the nation's largest. It began Tuesday in the San Gabriel Valley and East Los Angeles, then moves to the Westside and the South Bay cities Wednesday, and finishes Thursday in the Antelope Valley, San Fernando Valley, Santa Clarita Valley, the Los Angeles metropolitan area and South Los Angeles.
Pasadena, Glendale and Long Beach plan to conduct separate counts this week.
The 2009 census found that more than 48,000 people were homeless on any given night in the county. That was a 38% drop from 2007, a result met with skepticism among homeless services providers who said they were seeing more people — particularly families — because of the recession.
Advocates for the homeless will be watching to see whether the number has risen since then, especially because the economic downturn started worsening only a few months before the last count was conducted.
The total figure is primarily based on projections from sample census tracts, although some cities do a complete count.
Los Angeles Homeless Services Authority Executive Director Michael Arnold said the city and county have been investing in housing and other programs to get people off the streets, which could help account for the drop measured two years ago.
Methodological improvements have also helped the city-county authority "get closer to a true number," he said. In 2005, the count was based on results taken from about 20% of the total area. This year, Arnold expects to cover about 50%.
Nearly 4,000 volunteers have indicated that they would take part, and more are welcome.
"It's really a positive experience to see so many people from different parts of the community coming together on such an important issue," Arnold said in a statement. "The count is just the first step in my eyes to getting to the real goal of moving people into permanent housing."
A more detailed survey is planned in February to collect information on gender; ethnicity; the chronically homeless; veterans; homeless families; unaccompanied youth; people living with HIV, mental illness or substance abuse; and victims of domestic violence.