Oise is a department in the north of France. It is named after the river Oise. Inhabitants of the department are called Oisiens or Isariens, aft…Oise is a department in the north of France. It is named after the river Oise. Inhabitants of the department are called Oisiens or Isariens, after the Latin name for the river, Isara. It had a population of 829,419 in 2019.