The town of Jouars-Pontchartrain is located 35 km west of Paris, 18 km west of
Versailles and 22 km from
Rambouillet, on a buttress which delimits the western end of the plain of Versailles and at the foot from which begins the plain of
Montfort-l'Amaury. Its territory is irrigated by the
Mauldre whose south-north oriented course follows the eastern limit of the town and receives in the park of the
Château de Pontchartrain the Élancourt brook, a diversion of which feeds its pond. This brook, oriented east-west, is enlarged a little upstream by the Maurepas brook which joins it at Chennevières.
Hamlets of the municipality The commune comprises seven hamlets:{{cite web • Pontchartrain, in the north of the municipal territory, heart of the municipality, where are located, around the town hall, the Saint-Lin church and the Saint-Louis hospital, the majority of local shops and most of housing. • Chennevières, south-east of Pontchartrain and adjoining it. It is a residential and old hamlet, formerly a humid places where the culture of hemp prospered. • La Richarderie, to the east of Chennevières and adjoining it, is a semi-residential, semi-rural hamlet. • Jouars, away to the south of Pontchartrain, has a church and has only a few dwellings and rural farms. • Ergal, in the far east and on the edge of the municipal territory is adjoining the hamlet of Launay in the municipality of Élancourt, half-residential, half-rural. • Les Mousseaux, south of Jouars, on the edge of the municipal territory and adjoining the hamlet of Villeneuve (parc aux Loups) in the municipality of Maurepas, is half-residential, half-rural with a few small craft businesses. • La Dauberie, a very wooded residential area, is on the edge of Saint-Rémy-l'Honoré. The last two hamlets form a kind of enclave between the municipal territories of
Maurepas,
Coignières,
Saint-Rémy-l'Honoré and
Le Tremblay-sur-Mauldre. ==Population==