Seia is a municipality in Guarda District in Portugal. The population in 2021 was 21,755, in an area of 453.69 square kilometres. Its urban population is about 7,000. Seia was elevated to city status on 3 July 1986. The municipality is situated on the northwestern slope of Serra da Estrela, the highest mountain range in mainland Portugal, with a top height of 1993 meters. The present Mayor is António Luciano Silva Ribeiro, elected by the Socialist Party. The municipal holiday is July 3.