It was named after the Simplon Pass (Italian: Passo del Sempione).

Its territory corresponded with that of the present-day Swiss canton of Valais.

The department was created by Article 2 of the decree of 12 November 1810, reuniting the Valais to the French Empire.

This senatus-consulte is written as follows: The prefect (préfet) was the highest state representative in the department.

The commander of the troops stationed in the department was Étienne Félix d'Henin de Cuvillers.