The commune of Le Pecq is located in a loop of the Seine river, 19 km (12 mi) west of Paris, at the foot of the chateau of Saint-Germain-en-Laye.
Le Pecq's territory is astride the two banks of the Seine and includes a small island, Corbière. It is highly urbanized except for Corbière island, which is partially protected as a nesting zone for migratory birds. Until after the Second World War, there were swimming baths on the island. Le Pecq was famous for two other establishments related to water: a spa exploiting springs on St-Germain hill and a natural water swimming pool which was 100 metres long with sand beaches.
It borders the communes of Saint-Germain-en-Laye and Mareil-Marly in the west, Montesson and Le Mesnil-le-Roi (Carrières-sous-Bois district) to the north, Croissy-sur-Seine and Le Vésinet in the east and Marly-le-Roi and Le Port-Marly to the south.
The first mention of Le Pecq came in 704. In that year, the Merovingian king Childebert III granted a charter to Fontenelle Abbey which included territory in Aupec - the modern Le Pecq.
On 31 May 1875, a part of Le Pecq was detached and merged with parts of Chatou and Croissy-sur-Seine to create the commune of Le Vésinet.
The town in Le Pecq is notable for being the town of residence of Alain Gournac: Senator of the Yvelines for the Union pour un Mouvement Populaire (UMP) since 1995. A. Gournac also occupied the function of Mayor of the town between 1991 and 2013, year in which, following legislature forbidding Senators from also holding the title of Mayor, he was made to resign, leaving his seat to Laurence Bernard, also a member of the UMP.
The main transportation links in Le Pecq are the N13 which runs on the left bank of the Seine and secondary road D 186 connecting Saint-Germain-en-Laye with Paris which crosses the Seine at the Le Pecq bridge. This bridge was built in 1963. It has of flattened steel arches resting on two central concrete piers.
Le Pecq is not served by the Paris Métro, RER, or suburban rail network. The closest station to Le Pecq is Le Vésinet – Le Pecq station on Paris RER line A. This station is located in the neighboring commune of Le Vésinet, 1.2 km (0.75 mi) from the town center of Le Pecq.