Vallejo ( in English; [baˈjeho] in the original Spanish) is a city in Solano County, California, United States. As of the 2000 census, the city had a total population of 116,760. It is located in the San Francisco Bay Area on the northern shore of San Pablo Bay.

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 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. Vallejo has twice served as the capital of the State of California: once in 1852 and again in 1853, both periods being quite brief. Some of the first Europeans drawn to the Vallejo area were attracted by the sulfur springs; in fact, in the year 1902 the area was named Blue Rock Springs.