Socorro (So-kó-ro) was the name conferred by Don Juan de Oñate upon a Pueblo north of the present town of Socorro, the county seat. Some friendly Indians had presented him and his troops with corn in the summer of 1598, which is why he choose the name meaning "succor" or "help".

Created by the Territorial Legislature in 1852, Socorro County was once the largest in New Mexico, and has clearly had one of the least stable boundaries. Since its establishment under United States control, its area has been changed seventeen times, and its very existence was once threatened by legislative action. In the 1850's, Socorro County ran east-west between the Texas and California lines, taking in almost one quarter of New Mexico and most of southern Arizona. Subsequent subtractions have diminished the county to its present boundaries, while increasing those of seven others. In 1927, the State Legislature attempted to abolish both Socorro and Catron in order to create a new Rio Grande County. A court suit voided this act and the two counties retained their independence. Since it came into existence the Socorro County seat has been at the city of Socorro.

Among the county's earliest inhabitants were the Piro Indians, the most southerly of the Puebloans, and probably part of the Tiwa language group. Having come into the region in the 1200's, they lived in more than twenty villages in the Rio Grande Valley between La Joya and San Marcial, as well as in another area east of the river around Las Salinas. Their most prominent settlements were Senecú, Teypana, Alamillo, Sevilleta, Pilabó, and Qualacú. The Piros shared an uneasy occupation of the region with the Apache, who more often than not were hostile.

The county area and its Piro residents, located as they were along the Rio Grande route north from México, were visited by nearly all of the early Spanish explorers. In 1541, one of Coronado's officers and his men camped for a day near Teypana. Later in the sixteenth century the Chamuscado-Rodríguez and Espejo expeditions stopped in the Piro territory on their way north. In 1598, Juan de Oñate was a guest of the Piros, and recorded in his journal, "We halted for the night opposite Teypana, the pueblo which we called Socorro, because it furnished us with maize."