Santa Clarita Assemblywoman Christy Smith is trying to become the second consecutive Democrat to win what had been a seat long held by Republicans until Hill's 2018 victory over then-Rep. Steve Knight. Smith is facing Republican aerospace executive Mike Garcia.
Despite health risks amid the coronavirus pandemic, state law requires in-person voting to be available.
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California's 25th congressional district includes parts of Santa Clarita, Palmdale and Lancaster.
There are nine vote centers open from 7 a.m. to 8 p.m. Tuesday, seven in Los Angeles County, including at the Lancaster National Soccer Center, the addition of which late Friday drew the ire of Trump.
Los Angeles County's top election official is reassuring voters that substantial efforts are being made to ensure voting safety by sanitizing equipment after each use and employees at voting sites are wearing face coverings and gloves.
However, officials say every registered voter received a ballot in the mail and officials say so far based off ballots mailed in that turnout has been healthy.
One voter, though, said she never get a mail-in ballot.
"I'm registered but I didn't get a ballot," Valencia resident Olga Garcia said. "When I came in, everybody was keeping their distance like they're supposed to. Before I approached, (the voting center worker) cleaned it and wiped it down really well. There was no problem at all, then I went to my ballot site, it was all cleaned up. Everything was great."
In the interest of public health, both candidates have supported the mail-in ballot option.
"Through the wonderful thoughtfulness of our Secretary of State Alex Padilla and Governor Newsom, this is an all vote-by-mail ballot if people choose," Smith said. "So everyone received a ballot in the mail and can fill it out, drop it in the mail if they choose. But there will also be vote centers. Very grateful to hear that Los Angeles County is expanding to another vote center location."
That new vote center is located at the National Soccer Center in Lancaster.
The L.A. County Democratic Party claims they led the effort, in opening the new vote center in Lancaster, but the county registrar's office says the voting center was added at the request of the Republican mayor of Lancaster, R. Rex Parris, who tells Eyewitness News he's a big Mike Garcia supporter and has donated to his campaign.
"I had no idea that this was a partisan issue," Parris said. "It was Palmdale had two and hell, I want one. I just kind of thought we were being slighted."
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Garcia has said Smith is trying to steal the election. President Trump tweeted it's rigged because of the new Lancaster location, but there has been no evidence found to substantiate that claim.
Eyewitness News attempted to interview Garcia, an executive at Raytheon and Santa Clarita native, but we were told he wasn't available.
Smith, who has lived in Santa Clarita for 37 years, says she hopes to keep the purple district in the hands of Democrats and believes we need a proven leader to get us through COVID-19.
"The inherent risk of opening up too quickly is that we're right back on that upward trajectory with the infection rate which then taxes our public health system and so I would say we are on the right path," said Smith.
WATCH: Former Rep. Katie Hill breaks her silence after resignation: 'I strongly feel that I made the right call'
Hill announced her resignation Oct. 27 and it became effective Nov. 3, following the release of salacious photos online and allegations of an extramarital affair with a staff member.
The winner of Tuesday's election will serve out the balance of Hill's term. Garcia and Smith will square off again in the November election for the chance to serve a full two-year term.
City News Service contributed to this report.