The Ohlone Indians inhabited the Santa Clara Valley for centuries, before an expedition led by Spanish expolorer Gaspar de Portolá discovered the area in 1769. In 1777, the Valley's first mission and pueblo were established, beginning nearly a half-century of Spanish rule. The Mexican Revolution in 1821 triggered a new era of Mexican control. The same year that California was admitted to the Union--1850--Santa Clara County became one of the state's original 28 counties.