Vallejo is the largest city in Solano County, California, United States. The population was 116,760 at the 2000 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.

Vallejo is home to the Six Flags Discovery Kingdom theme park (formerly Marine World and Marine World Africa USA) ; the now-defunct Mare Island Naval Shipyard; the regional office for Region 5 of the United States Forest Service; the California Maritime Academy (part of the California State University system); the Vallejo Center campus of Solano Community College; and Touro University, an osteopathic medical college. Ferry service runs from a terminal on Mare Island Strait to San Francisco, through Vallejo Transit's BayLink division.