Ermoupoli, also known by the formal older name Ermoupolis or Hermoupolis, is a town and former municipality on the island of Syros, in the Cyclades, Greece. Since the 2011 local government reform, it is part of the municipality Syros-Ermoupoli, of which it is the seat and a municipal unit. It is also the capital of the South Aegean region. The municipal unit has an area of 11.181 km2.

Syros, also known as Siros or Syra, is a Greek island in the Cyclades, in the Aegean Sea. It is 78 nautical miles (144 km) south-east of Athens. The area of the island is 83.6 km2 (32 sq mi) and at the 2021 census it had 21,124 inhabitants.