During the 1960s, there were many municipal mergers across Norway due to the work of the Schei Committee.

After much debate in Mykland, a vote was held on whether or not to join Åmli to the north, Froland to the east, or Birkenes to the south.

On 1 January 1970, the uninhabited properties of Neset and Råbudal in Froland (which had been a part of Mykland until 1967) were moved to Birkenes municipality.

The first element is the genitive case of the word mikill which means "great" or "prominent".

The tables below show the historical composition of the council by political party.