Martinez is a city in and the county seat of Contra Costa County, California, in the East Bay of the San Francisco Bay Area. The population was 35,824 at the 2010 census. The city is named after Californio ranchero Ygnacio Martínez. The downtown is notable for its large number of preserved old buildings and antique shops. Martinez is located on the southern shore of the Carquinez Strait in the San Francisco Bay Area, directly facing the city center of Benicia and the southeastern end of Vallejo, California.
In 1824, the western side of Martinez, Alhambra Valley was included in the Rancho El Pinole Mexican land grant to Ygnacio Martínez. East of these lands was the Rancho Las Juntas, a grant made to Irish born William Welch in 1844; his land lay between the lands of Don Martinez and Don Pacheco.
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 way station for the California Gold Rush.