Val-d'Oise is a department in the Île-de-France region, Northern France. It was created in 1968 following the split of the Seine-et-Oise department. In 2019, Val-d'Oise had a population of 1,249,674. It is named after the river Oise, a major tributary of the Seine, which crosses the region after having started in Belgium and flowed through Northeastern France. Val-d'Oise is Île-de-France's northernmost department.