Osny is situated at the gateway to the Vexin, on both sides of the Viosne valley. It is surrounded by Pontoise, Cergy, Puiseux-Pontoise and Boissy-l’Aillerie.
Precious relics found in the area, such as stone tools, pottery and other mégaliths bear witness to a past dating back to antiquity and to constant activity right up to the present day. Numerous heritage elements form the background to everyday life in Osny, such as the Château de Grouchy, the Lameth column, or indeed the Chaussée Jules César, an important roadway in Roman times. Impressionist and post Impressionist painters like Camille Pissarro, Paul Gauguin, and William Thornley drew inspiration from the small rural village that was Osny in the 19th Century.
The population of Osny has grown considerably since the 1930s. This is due to the large number of activities which have become established, with the development of economic activity areas and commercial centres, but also in the town centre where small shops and businesses have sprung up.
Since 2014 and 2015 the Maison de l’Enfance, the Maison des Associations and the Médiathèque have increased the attraction of the town centre. Thus, due to its past and its present modernity, the town has benefited in its development from the happy combination of an existing heritage, a preserved environment and its belonging to the new Town.