Mendocino County is one of the original 27 counties. The county derived its name from Cape Mendocino, which was probably named in honor of either Antonio de Mendoza, Viceroy of New Spain, 1535-1542 (who sent the Juan Cabrillo Expedition to this coast in 1542), or Lorenzo Suarez de Mendoza, Viceroy from 1580 to 1583. Mendocino is an adjective form of the family name of Mendoza. Until 1859, its territory was administered by Sonoma County. Territory which at one time was in Mendocino County is now in Glenn, Humboldt, Lake, Sonoma and Trinity counties.

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