Clinton was the choice of 43 percent of county Democrats compared to 27 percent for U.S. Sen. Barack Obama and 10 percent for former North Carolina Sen. John Edwards.
Republicans preferred McCain by 2-to-1 over Mitt Romney with the Arizona senator being selected by 32 percent of respondents compared to 16 percent for the former Massachusetts governor. Former New York City Mayor Rudy Giuliani and former Arkansas Gov. Mike Huckabee tied for third with 9 percent each.
The poll of 800 registered county voters was taken between Jan. 10-14 and sponsored by the Silicon Valley Leadership Group.
"As an organization dedicated to civic engagement and community dialogue on important issues, and with the presidential primary just around the corner, we felt it was important to put our fingertips on the wrist of public opinion," Leadership Group Chief Executive Officer Carl Guardino said in a statement.
The poll has a margin of error of plus or minus 3.7 percent.
