Almost a week after Election Day, the nation is still awaiting California to complete its vote count. California, home to the majority of outstanding races crucial to determining the House’s balance of power, has attracted attention — and some criticism — for its lengthy counting process.

While many states processed most of their ballots shortly after polls closed on Tuesday, California began the weekend with nearly five million ballots left to count, about a third of the state’s total ballots cast.

Officials in California, the country’s most populous state, argue that this slower process is essential to accuracy and maximizes voter participation. They believe their expansive voter protections provide the public with more confidence in the outcome.

The delay in final results has left Americans questioning why the House’s balance of power is still unresolved, fueling opportunities for misinformation, with both Democrats and Republicans using the incomplete results to assert claims of voter fraud or tampering.

California’s voting system involves more than simply running ballots through a machine. The state is among a few nationwide that mails a ballot to every active, registered voter. Processing these mail-in ballots takes more time than in-person votes.

Election offices verify that each ballot’s envelope signature matches the voter’s signature on file. Instead of discarding incorrectly filled ballots, California election workers reach out to voters, allowing them time to correct errors and have their votes counted. Known as ballot curing, this process takes place in half of U.S. states, but it is particularly demanding in California, where most ballots arrive by mail or hand delivery.

Additionally, California counts ballots that arrive up to a week after Election Day, as long as they are postmarked by Election Day.

Two decades ago, only a third of California voters used mail-in ballots, allowing 81% of votes to be counted within two days after Election Day. In contrast, the March primary this year, in which nearly 90% of ballots were mail-in, saw only 59% counted within the same timeframe, per the nonprofit California Voter Foundation.

California grants counties 30 days to complete their vote count, a significantly longer period than most states. This extended timeline enables counties to determine their own counting speed and staffing levels, as long as they meet the final deadline, according to California Secretary of State Shirley N. Weber.

In a recent interview, Ms. Weber noted that Californians are accustomed to a slower count, with impatience mainly arising when national implications are at stake, as is currently the case.

“That’s not our problem,” she stated. “We’re counting as quickly as possible.”

California also has the largest share of outstanding ballots, and while Vice President Kamala Harris has received fewer votes nationwide than President Biden did in 2020, some Democrats and Republicans have taken the incomplete count as evidence of voter manipulation.

Professor Eric Schickler from the University of California, Berkeley, explained that even well-intentioned efforts to ensure a reliable election can be twisted into conspiracy theories. “There’s a lot of distrust in governmental institutions, which this only fuels,” he said.

Ms. Weber acknowledged that delayed results might lead to misinformation but suggested that speeding up the process might not prevent election conspiracies.

“They’ll do it anyway,” she remarked, emphasizing the goal of counting every vote accurately.

In 2022, it took two weeks to call a tight House race in Northern California. In 2018, a lengthy delay led then-Speaker Paul Ryan to question the integrity of California’s voting system when Republicans lost multiple House races they initially appeared poised to win.

This Monday, 10 of the 17 uncalled House races that will determine chamber control are in California, including key battlegrounds in Orange County and the Central Valley. Alameda County, which includes Oakland, has counted ballots slower than any other large California county, with only a third of votes counted two days post-election.

Alameda’s vote counting pace is determined by staffing levels approved by its board of supervisors, said Alameda County Registrar Tim Dupuis.

Election offices do not operate 24/7 during counting. Many adhere to standard business hours and take days off before completing their counts. Counties like Orange and Marin worked on Saturday and Monday, while Contra Costa took Friday off and resumed on Tuesday.

Kristin B. Connelly, Contra Costa County’s clerk-recorder, explained that her 120-person team operates with limited resources.

“We’re using all our equipment and staff to ensure accuracy, but space and resources are constraints,” she said.

Inside Los Angeles County’s expansive 144,000-square-foot building on Saturday, election workers verified signatures and inspected ballots manually.

Kim Alexander, president of the California Voter Foundation, noted that election offices have faced increased responsibilities and safety threats amid the rise in mail-in voting and political tensions.

A surge of last-minute ballots has further stressed counting efforts. Election officials across California reported a higher volume of Election Day ballots than in past years. In Los Angeles County, about four million people voted, with one million mail-in ballots dropped off on Election Day alone.

This influx, particularly in Marin County, created extra work as thousands of ballots arrived just before polls closed.

Mr. Schickler suggested that delays in California’s count might skew the public’s perception of the race’s outcome.