Sertã is a municipality in Castelo Branco District in Portugal. The population in 2011 was 15,880, in an area of 446.73 km. The presen…Sertã is a municipality in Castelo Branco District in Portugal. The population in 2011 was 15,880, in an area of 446.73 km. The present mayor is José Farinha Nunes, elected by the PSD. The municipal holiday is the June 24.