is a former municipality in Østfold
. It was originally a part of Aremark formannskapsdistrikt
(from 1837), but on July 1
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.
form of the name was Øyjamörk
. The first element is (probably) the genitive case of the old name of Øymarksjøen
), 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.