Sponsored Topics. Vallejo ( /vəleɪoʊ/ or /vəleɪhoʊ/; Spanish: [baʎexo]) is the largest city in Solano County, California, United States. The population was 115,942 at the 2010 census. It is located in the San Francisco Bay Area on the northeastern shore of San Pablo Bay. Vallejo is named for General Mariano Guadalupe Vallejo.