Älvsborg County initially encompassed the entire western half of Västergötland, and was named after Älvsborg Castle, which is where the county administration was initially based. Älvsborg was demolished in the 1660s and the county seat moved to nearby Gothenburg, but the county continued to bear the name Älvsborg. Under the 1658 Treaty of Roskilde, the Norwegian province of Bohuslen (Swedish: Bohuslän) was transferred to Sweden, and in 1680 it was decided to form a new county comprising Bohuslän and the western part of Västergötland, creating the new Gothenburg and Bohus County.[1]
The seat of Älvsborg County (which had become even more of a misnomer, as the site of the former Älvsborg fortress now lay within the new Gothenburg and Bohus County) therefore had to be moved again, this time to Vänersborg.[2]
