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 38,290 at the 2020 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.