Son is located at the Oslofjord, 50 kilometres south of the Norwegian capital Oslo, just north of Moss and near the border of Østfold, and is located west of the village of Hølen.

Son, together with the village of Hølen, was established as a municipality on 1 January 1838 (see formannskapsdistrikt).

On 1 January 1964 Son was merged with Vestby and then lost its status as a town (ladested).

On many Dutch maps from that time (the oldest being from 1582) the Oslo fjord is noted as Zoon Water.

Some distance up this river lies the parish Såner (Norse Sánar), and this name is most likely the plural of *Són.