Mountain House has been an unincorporated community for years.
It's just beyond the Altamont Pass, off Interstate 580 near Tracy.
On Monday, it officially became the state's 483rd city with the swearing-in of its own city council.
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Voters overwhelmingly elected to incorporate Mountain House in March.
It is the first new city in California since 2011.
"I'm just very thankful for all the help that we've had over the years, and I'm looking forward to continuing the growth of Mountain House," said Mountain House Mayor Andy Su.
The newly minted city will begin its legacy by hosting Independence Day celebrations on Thursday, including a parade followed by a city commemoration ceremony.