California Secretary of State Alex Padilla says, since January 1, nearly a million people have either registered or updated their information.
Elections officials predict interest will remain high, even though the state will no longer decide the Republican presidential nominee.
"I still expect a tremendous turnout above and beyond what may be typical for even a presidential election cycle," Padilla says.
Voters must register before midnight Monday to cast a ballot in the primary. They can register in-person at the DMV or county elections offices, online at registertovote.ca.gov, or by mail.
Voters who have listed No Party Preference, but who want to cast vote-by-mail ballots in the Democratic primary, must request them from their county elections offices by May 30.
CapRadio provides a trusted source of news because of you. As a nonprofit organization, donations from people like you sustain the journalism that allows us to discover stories that are important to our audience. If you believe in what we do and support our mission, please donate today.