The portion geest in the name refers to the geest lands, which were excavated in the seventeenth century for the benefit of the urban expansion of Leiden.
About the Oegst part more uncertainty exists. Different stories go about. The name was formerly often spelled Oestgeest or Oostgeest, which could indicate the geographical location of the village: east of the geest lands. However, the oldest spelling found in a copy of a list of goods of the St. Martin's Cathedral in Utrecht from the tenth century states Osgeresgeest. This could indicate an original resident and owner of the territory: Osger.
In the Middle Ages they also spoke of the Church of Kerckwerve if one referred to the Oegstgeester parish church (now the Green Church).
Oegstgeest is one of the earliest inhabited places along the coast. Evidence of a Batavian settlement from the second century was found in 1946 in an extension of a coastal dune in the Elgeesterpolder, although it is not certain whether this location remained permanently inhabited in the centuries after that.
By the 9th century there was already a little church in the same location as the current Little Green Church (Groen Kerkje) which, according to legend, was dedicated by Willibrord. The existence of this church is an indication that there may have been a community there.