Santa Ana County was one of the seven original partidos created in New Mexico under Mexican rule. Under U.S. rule, it became a U.S. Territorial county from 1852 until 1876, when it was absorbed by Bernalillo County. It does not exist today as an administrative unit. The original county seat of Santa Ana County is what is now Fort Defiance, Arizona. The county was named after Santa Anna, the ruler of Mexico throughout most of the mid-19th century.