It was founded as San Ambrosio de Ballenary by Ambrose O'Higgins in 1789, after his birthplace in Ballynary in County Sligo, Ireland.

Llanos de Challe National Park is located 60 km (37 mi) northwest of the city of Vallenar.

According to the 2002 census by the National Statistics Institute, Vallenar had 48,040 inhabitants (23,284 men and 24,756 women).

[2] As a commune, Vallenar is a third-level administrative division of Chile administered by a municipal council, headed by an alcalde who is directly elected every four years.

[1] Within the electoral divisions of Chile, Vallenar is represented in the Chamber of Deputies by Mr. Alberto Robles (PRSD) and Mr. Giovanni Calderón (UDI) as part of the 6th electoral district, (together with Caldera, Tierra Amarilla, Freirina, Huasco and Alto del Carmen).