Benicia is a city in Solano County, California, on the north bank of the Carquinez Strait in the North Bay region of the San Francisco Bay Area. It served as the capital of California for nearly thirteen months from 1853 to 1854. The population was 27,131 at the 2020 United States census. Benicia is just east of Vallejo and across the strait from Martinez.

The City of Benicia was founded on May 19, 1847, by Dr. Robert Semple, Thomas O. Larkin, and Comandante General Mariano Guadalupe Vallejo, on land donated to them by General Vallejo in December 1846. It was named for the General's wife, Francisca Benicia Carillo de Vallejo, a member of the Carrillo family of California, a prominent Californio dynasty. The General intended that the city be named "Francisca" after his wife, but this name was dropped when the former city of "Yerba Buena" changed its name to "San Francisco," so her second given name was used instead. In his memoirs, William Tecumseh Sherman contended that Benicia was "the best natural site for a commercial city" in the region.

In February 1848, first word of gold found at Sutter's Mill was leaked at a Benicia Tavern, thus starting the California Gold Rush. Benicia became a way station on the way to the Sierras.

In March 1850, Benicia became one of the first incorporated cities in California, a month after Sacramento. Benicia was the original county seat of Solano County. The lower floor of the Benicia Masonic Hall, built in 1850 with lumber donated by Benicia founder Robert Semple on land donated by Alexander Riddell, was used as the County court room and offices prior to the completion of Benicia's city hall. In 1858, the county seat was moved to Fairfield.

In 1853, Benicia became the third site selected to serve as the California State capital, after San Jose and nearby Vallejo, and its newly constructed city hall was California's capitol from February 11, 1853, to February 25, 1854. Soon after, the legislature was moved to the courthouse in Sacramento, which has remained the state capitol ever since. The restored capitol is part of the Benicia Capitol State Historic Park, and is the only building remaining of the State's pre-Sacramento capitols.

The original campus of Mills College was founded in Benicia in 1852 as the Young Ladies Seminary, and was the first women's college west of the Rocky Mountains. Before moving to Oakland in 1871, it was located on West I Street, just north of First Street.

From 1860 to 1861, Benicia was indirectly involved in the Pony Express. When riders missed their connection with a steamer in Sacramento, they continued on to Benicia and crossed over to Martinez via the ferry. One of the earliest companies in California, the Pacific Mail Steamship Company, established a major shipyard in Benicia in the 19th century. The prolific shipbuilder Matthew Turner formed the Matthew Turner Shipyard at Benicia in 1883. Benicia became an important wheat storage and shipping site. It was also the site of the United States Army's Benicia Arsenal.

On December 1, 1879, the Central Pacific Railroad rerouted the Sacramento-Oakland portion of its transcontinental line to Benicia and established a major railroad ferry across the Carquinez Strait from Benicia to Port Costa. The world's largest ferry, the Solano, later joined by the even larger Contra Costa, carried entire trains across the Carquinez Strait from Benicia to Port Costa, whence they continued on to the Oakland Pier.