With more than 50 percent of the vote, he avoids a runoff in November.
Simitian won 25,522 votes — 57.79 percent. His closest challenger, former Cupertino Mayor Kris Huyilan Wang, won 22.72 percent. In third place was Cupertino City Councilman Barry Chang with 19.49 percent.
Simitian said, "From my standpoint it's a happy result on two counts: a 35-point margin between me and my closest competitor, and a first-round victory, which means I don't have to go back to my supporters and ask for their help again in November.
"I think they'll be happy about that."
This will be Simitian's second stint on the county board, where he served from 1997 to 2000 before moving on to the California Assembly and later the State Senate.
He returns to the county level after being termed out of the State Senate.
The Palo Alto resident began his political career in the 1980s as a member of the Palo Alto Board of Education.