The voters whose ballots are in question used a drop-off location at Richmond City Hall on Oct. 12.
The voters have not been able to confirm their ballots were received, the county told ABC7.
Some ballots from that day and that same box were received, but others were not. Officials started figuring it out when voters tracked their ballots online, saw that they were not counted and began calling the office and posting on social media site Next Door.
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"I'm not worried that there's more, but I am worried that this happened," said Scott Konopasek, the assistant registrar of voters for Contra Costa County. "We have good plans, good procedures, good people and it is a little concerning. We can't explain what happened here but we know it was one box, one day and the voters are identifying themselves."
Elections officials do not know what happened to them, but do not believe foul play is to blame.
"Everyone's mind goes there. I can't imagine a scenario where there was foul play involved with destroying or losing half of the ballots from the box that day," said Konopasek.
The ballots may have just been misplaced in a warehouse, a county official said, though the affected voters have been issued new ballots.
In a statement, the City of Richmond said, "The County Election's Division is aware of the information regarding ballot theft being reported on social media and have no reason to believe it is true; however, they take these reports seriously."
In Contra Costa County, ballots at drop-off locations are collected daily by two employees and take three to four business days to be reported as received.
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Officials have searched the county cars used to drive to the boxes. Konopasek said they are alarmed the ballots haven't been found.
"We searched everywhere. We reviewed our practices. We reviewed our logs. To be honest right now we don't know exactly what happened," Konopasek said. "That's one problem, and we will get to the bottom of that. But the other immediate problem is these voters need to vote."
He said workers are trying to find everyone involved through phone calls and social media posts and are explaining to them how to vote in-person.
Konopasek said the system will not accept two votes from one person. If these people vote again and then the missing ballots are found and put into the system, he said the system will kick out the second vote.
Each drop-box is inspected daily for damage or tampering, according to the county.
"The ballot box at Richmond City Hall has been inspected by the county, and they have no reasons to believe that the box has been tampered with," the city's statement said.
The county has a total of 37 outdoor drop-off locations that are open 24 hours.
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Ballot drop boxes became available to Contra Costa County voters on Oct. 5, 29 days prior to Election Day.
Thirty-six percent of registered voters in the state, or nearly 8 million people, have already turned in their ballots.
All registered voters in California should have received their mail-in ballot in early October.
Ballots will have prepaid postage and can be returned at any time in California, including on Election Day.
A ballot can be received as late as Nov. 20 and it will still be counted, as long as it's postmarked no later than Nov. 3.
Californians can learn how to track their 2020 ballots here.
Get the latest stories and videos about the 2020 election here.
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