The trial, authorized by a law signed Aug. 15 by Gov. Jerry Brown, will study how mail-in voting affects election turnout and cost. A similar trial is underway in rural Yolo County.
As is done in Colorado, which changed to primarily mail-in voting in 2013, the trial will have at least one polling place open in each city, where voters can drop off a ballot or vote in person.
Under the trial, San Mateo County will hold three primarily mail-in elections before 2018. They will be off-year elections, such as for city council or school board races, or special elections. All registered voters in the test elections will receive a ballot in the mail and a prepaid return envelope.
The enabling legislation for this trial was authored by Assemblyman Kevin Mullin and state Senator Jerry Hill.
Because so many voters are already voting by mail, "it's time to examine our election system to be sure it is effective, efficient and accessible," Mr. Mullin said. He noted that in the June election, 78 percent of voters in San Mateo County voted by mail.
"By allowing an urban county to participate with a rural county in the pilot study, the reports produced for the Legislature will be more indicative of potential statewide effects," said Mark Church, San Mateo County's chief elections officer.
To help gauge the effect of mail-in voting on turnout, statistics on the numbers who vote in the mail-in elections will be collected by ethnicity, age, gender, disability, permanent vote-by-mail status, and political party affiliation.
Yolo County officials report that in its trial elections, it has saved as much as 43 percent of the cost of traditional polling place elections, but turnout results were inconclusive, Mr. Mullin's office said.