Martinez ( /mɑrtiːnɨs/ mar-tee-niss or /mɑrtiːnɛz/ mar-tee-nezz; Spanish: Martínez, meaning: Martinson) is a city and the county seat of Contra Costa County, California, United States. The population was 35,824 at the 2010 census. The downtown is notable for its large number of preserved old buildings. Martinez is located on the south side of the Carquinez Strait in the San Francisco Bay Area, directly facing the city of Benicia.
In 1824 the Alhambra Valley was included in the Rancho El Pinole Mexican land grant to Ygnacio Martínez. In 1847, Dr. Robert Semple contracted to provide ferry service from Martinez to Benicia, which for many years was the only crossing on the Carquinez Strait. By 1849, Martínez served as a weigh station for the California Gold Rush. The town was laid out in 1849 by Col. William M. Smith and named for Martinez. It became the county seat in 1850, but could not incorporate at the time because it lacked the 200 registered voters required, and only became a city in 1876.
Martinez was the home of John Muir from 1880 until his death in 1914. He was buried about a mile south of the building that is now the John Muir National Historic Site. Also nearby is the Vicente Martinez Adobe, built in 1849 by the son of Ygnacio Martinez.