Monday is the last day to register to vote in order to cast a ballot or vote by mail in the Nov. 6 general election.
Residents of California have until midnight to register, or update their registration if they have moved or changed their names, according to California Secretary of State Alex Padilla.
Those who are unsure of their voter registration status can check it at voterstatus.sos.ca.gov.
"This election will have a major impact on our nation, our state, and our local communities in the coming years -- make sure your voice is heard," Padilla said in a statement.
Online voter registration is available at registertovote.ca.gov.
The website is mobile-friendly, so residents can register from their smartphone or tablet.
Online voter registration is available in 10 languages: English, Spanish, Chinese, Hindi, Japanese, Khmer, Korean, Tagalog, Thai and Vietnamese.
Paper voter registration cards are available at most government offices, including libraries and post offices. Paper voter registration cards must be postmarked by Monday's deadline.
In Alameda County, Registrar of Voters Tim Dupuis said workers will be staffing the office until midnight to register eligible voters. About 850,000 voters are now registered in the county, Dupuis said.
Californians must re-register to vote if they move to a new permanent residence, change their name, or want to change their choice of political party.
There is an option for California residents who do not register or update voter registration information by Monday's deadline. Under conditional voter registration, eligible residents can go to their county elections office or a designated satellite location to register and vote.
The conditional voter ballots will be counted once the county office has completed the voter registration verification process.
Voters can complete the conditional voter registration process from Oct. 23 up to Election Day on Nov. 6.
Voters in Napa, San Mateo, Madera, Nevada, and Sacramento counties can access conditional voter registration at any Vote Center in their county.