Sines regained municipal autonomy and new postal headquarters following the Republic

The establishment of the Portuguese Republic brought significant administrative and structural changes to Sines, most notably the restoration of its municipal autonomy in 1914 after 59 years of being annexed to Santiago do Cacém.

A key example of this reorganization was the repurposing of the former Igreja de Santa Isabel to serve as the first headquarters for the Correios e Telégrafos (Post and Telegraphs). Following the Law of Separation of State and Church, the Sines Municipal Council acquired the 18th-century temple in 1921. After adaptation works, the building was used for postal services starting in 1927. The municipality re-acquired the property in 2011, preserving its historical documentary collection.