SACRAMENTO, Calif. (AP) -- California's June primary saw the highest percentage of voter turnout in a midterm primary election since 1998.
More than 37 percent of registered voters cast ballots in the primary. That's up more than 12 percent from the previous midterm primary in 2014, when turnout hit a record low. The June turnout was closer to levels in the 2010 and 2006 primaries, when 33 percent of registered voters participated.
California Secretary of State Alex Padilla certified the results Friday.
"While these numbers show great progress, we know that we still have more work to do," Padilla said.
California's high-profile contests for governor and U.S. Senate likely helped increase turnout, said Mindy Romero, director of the California Civic Engagement Project at the University of Southern California.
California typically ranks in the bottom fourth of states in turnout, Romero said. The numbers this year are promising, but not high enough to dramatically shift the state's ranking compared to other states, she said.
"They're good for what we've seen historically, but they're still low numbers," Romero said. "There's this opportunity to build on this good primary and hopefully have a very strong November."
Turnout is typically lower in primary elections than general elections. It also is typically lower in midterm years than in years with a presidential election.
In Sacramento, Nevada, San Mateo, Madera and Napa counties, all registered voters were mailed a ballot in the hopes of boosting turnout.
Voters in those counties could mail back their ballots or put them in drop boxes. They could also vote in person at a county vote center.
In the five counties using the new voting model, turnout increased from 2014. All but one also saw an increase from 2010. But the increases were roughly on par with those seen statewide, except in San Mateo where turnout jumped roughly 17 percent from 2014. Madera saw the smallest increase from 2014 at nearly 8 percent.
It was the first time counties used the model for a statewide election. It's too soon to determine whether the new model will boost turnout in the long run, Romero said.
Padilla said the results in the five counties were positive and that he anticipates several more counties will adopt the model in the near future.
Among all eligible California voters, including those who aren't registered, about 28 percent participated in the primary, Romero said.