Agder is a county (fylke) and traditional region in the southern part of Norway[4] and is coextensive with the Southern Norway region. The county was established on 1 January 2020, when the old Vest-Agder and Aust-Agder counties were merged.[5] Since the early 1900s, the term Sørlandet ("south country, south land, southland") has been commonly used for this region, sometimes with the inclusion of neighbouring Rogaland. Before that time, the area was considered a part of Western Norway.[6]
The area was a medieval petty kingdom, and after Norway's unification became known as Egdafylki and later Agdesiden, a county within the kingdom of Norway. The name Agder was not used after 1662, when the area was split into smaller governmental units called Nedenæs, Råbyggelaget, Lister, and Mandal. The name was resurrected in 1919 when two counties of Norway that roughly corresponded to the old Agdesiden county were renamed Aust-Agder (East Agder) and Vest-Agder (West Agder). Even before the two counties joined in 2020, they cooperated in many ways; the University of Agder had sites in both Aust-Agder and Vest-Agder, as did many other institutions, such as the Diocese of Agder og Telemark, the Agder Court of Appeal, and the Agder Police District.
The name Agder is older than the Norwegian language. Its meaning is not known. Just as the Norwegian language derives from Old Norse, Agder derives from the Old Norse word Agðir. In the early Viking Age, before Harald Fairhair, Agðir was a petty kingdom inhabited by a people named after it, the Egðir.[6]
Nothing in Old Norse gives any hint as to the word's meaning; it was not produced (from known segments) in Old Norse, which means the name is older still. The Egðir are believed to be the same etymologically as the Augandzi people mentioned in the Getica of Jordanes, who wrote of Scandza (Scandinavia) in the 6th century. If Jordanes's Scandza is a palatalized form of *Scandia, then Augandzi is likely a palatalized form of *Augandii, residents of *Augandia.[7]
A name of that period would have to be closer to Proto-Germanic; in fact, a word of that period does present itself and fits the geographical lore of the times: *agwjō (meaning "island"),[8] which Jordanes and all his predecessors writing of Scandinavia believed it to be. A simple metathesis produces a possibly late form, *augjo-, but this derivation is speculative. There is no other evidence on Auganza, and its connection to Egder is hypothetical too.
On 1 January 1838, the formannskapsdistrikt law went into effect, creating local municipalities all over Norway. The municipalities have changed over time through mergers and divisions as well as numerous boundary adjustments. When Agder county was established on 1 January 2020, it had 25 municipalities.