It was a lower regional level subdivision, usually corresponding to a Swedish county.
A defence district was the lowest regional unit in the Swedish Armed Forces.
Such were found in particularly important coastal areas during World War I and from 1939 on at a time of mobilization.
[3] The district was responsible for defence planning, home defence, supervision of fixed facilities, certain territorial units and the Home Guard equipment and equipment.
Situation after 1973-76's creation of the defence district regiments:[3] The organisation in 1997:[3]