The San Francisco Chronicle says state prosecutors filed two felony counts on Thursday against 61-year-old Stuart Forrest, who led the county probation department for three years.
The complaint says Forrest possessed child pornography on Dec. 20 and 21.
Forrest was placed on paid leave on Dec. 21 and he retired 10 days later.
District Attorney Steve Wagstaffe says he felt it was appropriate for the state attorney general's office to prosecute the case because of the probation department's close relationship with his office.
A relative told the Chronicle that Forrest wasn't available for comment.