Usually, the Counties of Norway are called either fylke or amt depending on which time period is researched.
The historical counties called amt were in use from 1662 to 1919. Before the counties/amt there was len and syssel. (Wikipedia about Syssel)
The modern-day counties in Norway are called fylke and are sub-national, geographical areas between the state and the municipalities. The counties called fylke were established in 1919 as a continuation of the former counties called amt, but with mostly new names. The 20 counties listed below are what the National Archives of Norway have used as base to find the parish books used for research. Therefore they are also the basis for the Norway Location Categories.
There were 20 counties/fylke 1919-1972; Akershus fylke, Aust-Agder fylke, Bergen fylke, Buskerud fylke, Finnmark fylke, Hedmark fylke, Hordaland fylke, Møre og Romsdal fylke, Nordland fylke, Nord-Trøndelag fylke, Oppland fylke, Oslo fylke, Rogaland fylke, Sogn og Fjordane fylke, Sør-Trøndelag fylke, Telemark fylke, Troms fylke, Vest-Agder fylke, Vestfold fylke and Østfold fylke.
In 1972 Bergen fylke was merged into Hordaland fylke. In 2018 Trøndelag fylke was created and Sør-Trøndelag fylke and Nord-Trøndelag fylke were merged into Trøndelag fylke.
From 1 January 2020, Norway is divided into eleven counties/fylke, these are: Oslo, Rogaland, Møre og Romsdal, Nordland, Viken, Innlandet, Vestfold og Telemark, Agder, Vestland, Trøndelag and Troms og Finnmark.
From 1 January 2024, Norway reversed some of the county mergers that occurred in 2020 and is now divided into fifteen counties/fylke, these are: Oslo, Rogaland, Møre og Romsdal, Nordland, Østfold, Akershus, Buskerud, Innlandet, Vestfold, Telemark, Agder, Vestland, Trøndelag, Troms and Finnmark.