Saint-Prix (French pronunciation: [sɛ̃ pʁi] ⓘ) is a French commune located in the Val-d'Oise department, in the Île-de-France region.

The commune is located 15 km to the north of Paris, on the southern flank of the vast butte-témoin bearing the forest of Montmorency.

The Hellenist, epigrapher and archaeologist Bernard Haussoullier (1852–1926) died in Saint-Prix.

Attested as Turnus in 1175, Tour or Tourn, To or Torn in 1193, Tou in 1648, Thou in 1691.

Formerly "Thor" or "Thür", of Germanic origin (compare Thor), the village owes its current name to the Auvergne saint Praejectus martyred in 676 AD, whose relics were deposited in a priory established by monks who had received them from Jean de Tour, treasurer of the Temple of Paris.