The town of Mysen was separated from Eidsberg to form a municipality of its own on 1 July 1920 .
Eidsberg was merged back into the municipality of Eidsberg on 1 January 1961 .
The town of Mysen was separated from Eidsberg to form a municipality of its own on 1 July 1920 , but it was merged back into the municipality of Eidsberg on 1 January 1961 .