The Governorate of the Río de la Plata (Spanish: Gobernación del Río de la Plata) was one of the governorates of the Spanish Empire. It was created in 1549 by Spain in the area around the Río de la Plata.

Governors of New Andalusia

• Adelantado Governor, Captain General, and Chief Justice Pedro de Mendoza (1534–1537). First founding of Buenos Aires; Ft. Corpus Christi founded by Juan de Ayolas. Retires and dies mad en route home.
• Governor Juan de Ayolas(1537–1539). In Paraguay. Asunción founded by Gonzalo de Mendoza. Killed by Indians.
• Lt. Governor Francisco Ruíz Galán (1537–1541). At Buenos Aires, prior to its abandonment.
• Governor Domingo Martínez de Irala (1539–1541). Elected by the colonists.
• Adelantado Governor Alvar Núñez Cabeza de Vaca (1541–1544). Victorious campaign against Guarani in 1542. Arrested and returned to Spain for trial.

Governors of the Rio de la Plata

• Governor Domingo Martínez de Irala (1544–1556). Encouraged his men to marry and keep concubines from local women. Two adelantados are unable to arrive from Spain and de Irala confirmed in his post by the king 1552. Died peacefully.
• Governor Gonzalo de Mendoza (1556–1558). Ciudad Real de Guayrá founded by Ruy Díaz de Malgarejo in 1557. Died peacefully.
• Governor Francisco Ortiz de Vergara (1558–1569). Elected by the colonists. Foundations fail at San Francisco, Sancti Spiritus, and Santa Cruz de la Sierra. Arrested and returned to Spain for trial.
• Lt. Governor Felipe de Cáceres (1569–1572). Appointed by Royal Audience. Arrested and returned to Spain for trial.
• Adelantado Governor Juan Ortiz de Zárate (1572–1576). Sailed to Spain to confirm his election. Foundation of Tucuman.
• Lt. Governor Diego Ortiz de Zárate (1576–1578). Juan Ortiz leaves administration to his daughter Juana, but others de facto governors.
• Lt. Governor Juan de Garay (1578–1583). Buenos Aires refounded 1580.
• Lt. Governor Alonso de Vera y Aragón (1583–1587). And de facto governor at Asunción until 1592.
• Adelantado Governor Juan Torres de Vera y Aragón (1587–1592). Judge of the Royal Audience, married to Juana Ortiz de Zárate. Last appointed adelantado.

Governors of the Rio de la Plata and Paraguay

• Governor Hernando Arias de Saavedra ("Hernandarias") (1592–1594).
• Governor Fernando de Zárate (1594–1595).
• Governor Juan Ramírez de Velasco (1596–1597).
• Governor Hernando Arias de Saavedra (1597–1599). Second time.
• Governor Diego Rodríguez de Valdés y de la Banda (1599–1600).
• Governor Francés de Beaumont (1600–1602). Appointment formalized 1601.
• Governor Hernando Arias de Saavedra (1602–1609). Third time. First Jesuit Reduction established. Slave trade restricted.
• Governor Diego Martín de Negrón (1609–1613).
• Governor Mateo Leal de Ayala (1613–1615).
• Governor Hernando Arias de Saavedra (1615–1617). Fourth time. Guayrá (Paraguay) separated into a separate governorate in 1617.

1. Governors of Rio de la Plata

Sources

1. Wikipedia article in English on Governorate of the Río de la Plata
2. Wikipedia article in English on Dom Pedro de Mendoza
3. Wikipedia article in English about Juan de Ayolas