Øymark is a former municipality in Østfold county, Norway. It was originally a part of Aremark formannskapsdistrikt (from 1837), but on July 1, 1903 Øymark was separated from Aremark to form a separate municipality. At that point Øymark had a population of 1 832.

On January 1, 1964 Øymark was merged with Rødenes to form the new municipality Marker. Before the merger Øymark had a population of 2 091.

The name

The Norse form of the name was Øyjamörk. The first element is (probably) the genitive case of the old name of Øymarksjøen (Norse *Øyi), the last element is mörk f 'woodland, borderland'. The old name of the lake is derived from øy f 'flat and fertil land along a waterside'.

Until 1918 the name was written Ømark.