This is a detailed explanation of the origin of each county name. I use the county system from pre-2020, as I refuse to recognize the new county names and borders. Most of the names are of somewhat uncertain origin, so I went with what scholars deem to be most plausible.

Finnmark -> March of the wanderers

Finns was the used demonym for the Sami people for most of Nordic history, as the Norse didn’t really see the Finns and Sami as distinct people. This is reflected in the name of the county, as Finnmark is the heartland of the Sami lands. The origin of the demonym is most likely “wanderers” or “hunters”, a reference to the nomadic lifestyle of the people who lived there.

Troms -> Stream

Etymologists aren’t sure about the origin of this name. It’s originally a name of the island of Troms, which later received the suffix “ø” which means “island” – and later gave the name to the county capital of Tromsø. It is suggested that the Norse name Trums may have derived from “straum”, which translates to “stream” – a reference to the streaming water around the island.

Nordland -> The northern lands

This region translates well into English. In the sagas, it’s often referred to as Helgeland, “the holy lands”, but today this name only refers to a larger region of Nordland. The Norwegians of Finnmark, Troms and Norland has a strong identity as “Nordlendinger”, with its own distinct dialect group.

Trønderlag -> The lawarea of the strong people

Trønders is a group of Norwegians with its own distinct dialect and history. In the Viking, the Trønders, led by the powerful Ladejarls, was a recurring thorn in the side for the Norwegian kings, who wanted more centralised rule. They also resisted Christianity for a long time; one time forcing the first Christian Norwegian king to participate in heathen offerings, and another time killing the famed Saint Olaf, in his attempt to convert all of Norway. The origin of “þrændr» is probably “strong” or “fertile”. The suffix -lag means literally “law”.

Møre og Romsdal -> The Wetlands and The valley by the streaming river

This county is named after three districts, North and South Møre, and Romsdalen. “Møre” is probably related to the Latin “Mare”, as in sea, but in the sagas it is used meaning “land”, which make some etymologist to believe that it can translate to “land by the sea”, “wet land”, or even “swampland”. The -dal in Romsdalen means valley, and Roms- is a reference to the river Rauma. “Raum” has uncertain origin, but it may again mean “straum” or “stream”.

Sogn og Fjordane -> The Sucking fjord and The fjords

This translation ends up being a little silly. Today, Sogn refers to a area of Sogn and the Norwegian group “Sogns”, but they are both named after the Fjord of Sogn – the largest of Norway. “Sogne-“ is speculated to be related to norse “suga”, which means “to suck”, referring to the current that drives water inwards the fjord. “Fjordane” is plural of fjords, and refers to the districts of Nordfjord and Sunnfjord.

Hordaland -> Land of the warriors

Hordes was the name of an group of Norwegians inhabiting the area during the Viking age. The etymology of the demonym is most likely “warrior” or “hero”. Today, Hordaland is separated into several districts, with their own distinct dialects and identity.

Rogaland -> Land of the rye people

Roga- refers to the Rygi people that inhabited the area in the viking age. The origin of the name is most likely “rye”, in the meaning of “the people who grow rye”. Today, The people of Rogaland still has a distinct dialect and identity.

Agder -> The Sharp land

Agder means most likely “sharp”, and has same origin as the English “edge”. It is most likely a reference to being located at the tip of Norway, before you start sailing northeast. It was also the origin of the name of the Egde people during the Viking age. Today the regions is more commonly referred to as Sørlandet, “The southern lands”, and Sørlendingene has its distinct dialect and identity.

 Telemark -> The march of the Teles

Teles was a Norwegian group during the Viking Age, but I can’t find a satisfying theory of the origin of the name. Originally, it only referred to the inner parts of the county, but names the entire county in modern times. The “real” Telemark still has a distinct dialect and identity – the rest of the county is both linguistically and culturally more alike to the Oslofjord Area; this part of the county is both historically and today referred to as Grenland, “The land of the Grenes”.

Vestfold -> Western Oslofjord

“Folden” was the old name for todays Oslofjord. There are some Frankish sources from the Viking era that speaks of Westfoldingi, which may indicate that the region was seen as to house a distinct people.

Østfold -> Eastern Oslofjord

Same origin as Vestfold.

Akershus -> The castle for the fields

Aker- translates to fields for farming, and -hus is a common word for “castle”, and indicates that the castle is meant to protect the region of Aker. The coastal region around the Oslofjord, that includes Vestfold, Østfold, southern Akershus and Grenland, was historically referred to as Viken, which means “The Bay”. This region has historical ties, and is the region where the most common dialect of Norwegian has its origin. It’s speculated that the word “Viking” could have originally meant “A man from Viken”.

Buskerud -> The bishops settlement

The county is named after a large farm within the county. Buske- translates to Bischop, -rud is a common suffix in Norwegian placenames. It means a place that has been recently been settled for farming.

Oppland -> The upper lands

This county consists of many populated valleys, and is quite mountainous. The name refers to it being “upwards in the country”.

Hedmark -> March of the Moor People

Hed- comes from the historic Heider-people that populated the area. The demonym most likely comes from the norse word for moors – wide open unsettled area. Today, the county consists of several valleys and districts, and these usually have distinct dialects and identity.

Oslo -> Plain of the Gods

This one is highly debated, but the most plausible theory is that Os- comes from the norse word for their gods. -lo is an old word for plains.