The history of the district is connected with the history of Holstein. In 1134 the castle of Segeberg was erected as a regional centre from where the reeve of Segeberg ruled. When Schleswig-Holstein became a Prussian province in 1865, the Prussian administration established the district of Segeberg.
Since then the district has considerable grown twice: In 1932 parts of the dissolved district of Bordesholm joined the district; and in 1970 the city of Norderstedt became part of the district.
The district of Segeberg consists of the agricultural plains between the cities of Neumünster and Hamburg. A southwestern portion of the hilly lakeland called "Holsteinische Schweiz" (Holsatian Switzerland) belongs to the district, as well as some northern suburbs of Hamburg.