The homeless population in Orange County has grown since the last official check two years ago, according to results from the 2015 biennial homeless census.

More than 980 volunteers carrying out the point-in-time homeless count tallied 4,452 homeless people one night in January. That’s a 5 percent increase compared with the 2013 homeless census.

Using the point-in-time count, Orange County officials estimate that nearly 15,300 people will experience homelessness at least one night over the course of the year. That’s a 20 percent increase compared with the 2013 estimate of 12,707.

A summary of the homeless count results were released Monday at a meeting of the Orange County Commission to End Homelessness.

“The big difference we saw between this year and 2013 was the weather,” said Karen Williams, executive director of 211OC, the organization in charge of the Orange County homeless census.

Williams said the homeless count in 2013 was conducted after three days of bad weather, which she said probably forced people into hiding, making them harder to count. This January, the weather was warmer and windy during the count, so more homeless may have slept outside, she said.

Williams noted that volunteers also found larger encampments at the Santa Ana Civic Center, along the Santa Ana River Trail and around the federal building in Aliso Viejo.

"People were congregating more," she said. "We think that made a big difference."

Half of the homeless counted this year were unsheltered, meaning they were sleeping on the streets, in tents or in cars. The other half were sleeping in a shelter or some type of transitional housing.

Williams said her organization and county staff will continue to review the numbers to try to better determine what’s behind the increase. She said some early ideas include higher rents forcing people onto the street and more people released from jails and prisons under Prop 47 and realignment.

A full narrative report on this year’s homeless count is due next month.

The homeless census is important for municipalities when applying for federal funding from the Department of Housing and Urban Development.

Los Angeles County also saw an increase - a 12 percent jump - in the number of homeless people counted during this year's census compared with 2013. The count estimated 44,359 homeless in Los Angeles County, about 70 percent of them unsheltered.