Mariposa County was one of the original twenty-seven counties created in California when the boundary lines were drawn in 1850. At that time it occupied more than one-fifth of the state’s area or approximately thirty thousand square miles. Stretching from the Coast Range to the present Nevada state line, and touching Los Angeles County on the south, Mariposa County unwillingly became the “Mother of the Counties,” as huge parcels of land were annexed away to create six new counties and add pieces to five others. It was eventually whittled down to it present size, a mere 1,455 square miles. The county seat was moved here on November 10 of 1851 from the nearly abandoned Agua Fria, which had lost most of its population to the rapidly expanding Mariposa.

Although he never lived in Mariposa, Colonel John C. Frémont—the famed explorer, army officer, and presidential candidate—had a major influence on local events. In fact, he at one time owned the entire town as it was located within the boundaries of his vast, forty-four thousand acre Mariposa Land Grant.