Ptolemaic Kingdom
Despite the incorporation of Kos to the Ptolemaic Kingdom, the island kept it political autonomy (shown thanks to a 3rd century's BC decree, found at Kos and well studied by some Greek's history specialists). The island was ruled by itself, thanks to it citizen's assembly and magistrates (the monarch, the prostates, the exegetes, etc). The fact that the city could legislate decrees and apply its own laws shows political independence regarding the Ptolemaic kingdom. The city-state stay in control of its political institution and its civil rights.