Val-d'Oise (French pronunciation: [val dwaz]) is a French department, created in 1968 after the split of the Seine-et-Oise department and located in the Île-de-France region. In local slang, it is known as "quatre-vingt quinze" (i.e. "ninety-five") or "neuf cinq" (i.e. "nine five"). It gets its name from the Oise River, a major tributary of the Seine, which crosses the region after having started in Belgium and flowed through north-eastern France. Paris-Charles de Gaulle Airport, France's main international airport is partially located in Roissy-en-France, a commune of Val d'Oise.

The original departments of France were established in 1790 when the French National Assembly split the country into 83 departments of roughly the same size and population. They were designed as sets of communes, and when better maps became available, certain revisions had to be made. After defeat by the Prussians in 1871, certain territories were ceded to them and some rearrangements made. In 1955 and 1957, some departments changed their names. In 1964, it was determined to divide up the departments of Seine and Seine-et-Oise. Val-d'Oise was one of the new departments so formed, and was created entirely from the previous department of Seine-et-Oise.

Val-d'Oise is a department in north central France and is part of the region of Île-de-France. To the south of the department lies the department of Hauts-de-Seine, to the southwest lies Yvelines, to the west lies Eure, to the north lies Oise, to the east lies Seine-et-Marne and to the southeast lies Seine-Saint-Denis. The official préfecture (capital) of the department is the commune of Pontoise, situated in the suburbs of Paris some 28 kilometres (17 mi) northwest of the centre of the city, but the préfecture building and administrative offices are in the neighbouring commune of Cergy. The River Oise is a right tributary of the River Seine, and flows through the province from northeast to southwest.

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