Sirdal is a municipality in Vest-Agder county, Norway. Sirdal was separated from Bakke in 1849. Sirdal was divided into Tonstad and Øvre Sirdal on 1 January 1905, but these were again merged to recreate Sirdal on 1 January 1960.It is the northernmost valley in Vest-Agder. At the north end of its long narrow lake, Siredalsvatn, lies the administrative center of the municipality in the village of Tonstad. Bjørnestad is another village lying in Sirdal.