On 1 January 1868, a small part of Finnaas (population: 10) was transferred to the neighboring municipality of Fitje.

On 1 April 1870, the Øklandsgrend area (population: 247) was transferred from Finnaas to the neighboring municipality of Stord.

The spelling of the name changed slightly over time from Findaas to Finnaas and then finally to Finnås.

[5] The municipality (originally the parish) is named after the Finnaas farm since the Old Moster Church was built there.

On 21 December 1917 (after the municipality had been dissolved and merged into Bømlo), a royal resolution enacted the 1917 Norwegian language reforms.