Supervisor John Gioia was sworn in as vice chair.
Bonilla thanked outgoing chair Supervisor Federal Glover for his leadership throughout 2008, a difficult year for the supervisors, who were forced to make many difficult decisions, including major cuts to the county's budget.
"We are deeply grateful for Federal's leadership," Bonilla said.
She described Glover as a "peacemaker" and a careful and thoughtful leader.
Presiding Judge Mary Ann O'Malley also formally swore in supervisors Gayle Uilkema, Mary Piepho and Glover, who were re-elected in November.
