Trump and J.D. Vance are leading in San Joaquin County, Stanislaus County, Merced County, and Fresno County.
Voters in all of those counties backed President Biden just four years ago.
Now, they are behind President-Elect Trump.
"Basically, it's the economic issue," Fresno State political science professor Thomas Holyoke said. "It's inflation."
"Harris didn't seem to really speak to the issue. So in frustration, people seem to have turned to Donald Trump for a second try," he added.
Political consultant Henry Perea says President-Elect Trump's message about the economy reached Central Valley Democrats, too.
"I think you had a lot of Democrats, I think you had a lot of Republicans coming together and saying maybe we do need to see something different in our region," Perea said.
President-Elect Trump's support in the Valley comes as voters decided on key measures statewide.
They decided to get tough on crime by passing Proposition 36, rejecting raising the minimum wage and upholding forced labor in prison.
"On the economic issues, they were not in favor of rent control," Holyoke said.
"Of course, on the other hand, they did approve two very expensive bond issues and enshrined, you know, the right to marriage generally for all kinds of people in the California Constitution."
California election results will not be certified for weeks. In Fresno County, officials are still working through about 95,000 vote-by-mail ballots.
Holyoke says Democrats are typically more likely to vote by mail.
However, this year, Trump also encouraged his supporters to vote early.
"Probably out of the ballots that are yet to be counted -- probably a good portion -- perhaps the majority are Democrats," Holyoke said.
"I don't think Fresno County will flip back blue again, but I think the gap will close."
Holyoke says that if President-Elect Trump does not quickly deliver on his economic promises, his Central California supporters could abandon their support.
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