SAN DIEGO -- The County of San Diego on Friday began offering free tax preparation to low-income families and individuals as part of its annual Earned Income Tax Credit campaign.

Throughout April 18, more than 400 volunteers will file the returns electronically at about 80 locations throughout the region, said Jose Alvarez, who is with the Health and Human Services Agency. An appointment can be made by calling 211, he said.

"In these difficult times, we want to help low-income families and individuals who are struggling to make ends meet," said Greg Cox, vice chairman of the county Board of Supervisors.

The campaign was launched by the county's Health and Human Services Agency in 2003 to get residents to take advantage of the federal Earned Income Tax Credit designed to help low-income individuals and families keep more of their wages, although the IRS estimated about 20 to 25 percent of those eligible do not claim the credit, Alvarez said.

Families and individuals who worked in 2011 and earned less than $48,500 could qualify for as much as $5,600 in EITC credit, Alvarez said, noting about $77 million in EITC dollars go unclaimed by county residents each year.

Last year, more than 43,000 federal and state returns were filed as part of the campaign, which brought about $25 million back to local residents, almost $8.2 million of that from EITC funds, Alvarez said.

Also as part of the campaign, students from San Diego State University, Cal State San Marcos and Southwestern College will screen families and individuals for CalFresh eligibility. Alvarez said.