Izola was attested in written sources asInsula in 972 and 977, and asInsulle in 1281. The nameIzola is borrowed fromItalianIsola, literally 'island', referring to the fact that the town center is a former island that was artificially connected with the mainland at the beginning of the 19th century.[2]
Anancient Roman port and settlement known asHaliaetum stood to the southwest of the present town, next to the village ofJagodje, as early as the 2nd century BC. The town of Izola was established on a small island by refugees fromAquileia in the 7th century. The coastal areas of Istria came underVenetian influence in the 9th century. The settlement was first mentioned in writing asInsula in a Venetian document entitled Liber albus in 932 AD.[3] It became definitely the territory of theRepublic of Venice in 1267, and the centuries of Venetian rule left a strong and enduring mark on the region. The Venetian part of the peninsula passed to theHoly Roman Empire of the German Nation in 1797 with theTreaty of Campo Formio, until the period ofNapoleonic rule from 1805 to 1813 when Istria became part of theIllyrian provinces of the Napoleonic Empire. After this short period, during which Izola's walls were torn down and used to fill in the channel that separated the island from the mainland, the newly establishedAustrian Empire ruled Istria until November 1918.[4] The treaty of Saint Germain assigned Izola and the rest of the Istria region to Italy. The Italian-speaking population was the majority according to the Austro-Hungarian census of 1900: of 5,363 inhabitants, 5,326 spoke Italian, 20 Slovene, and 17 German. Istria became part of theKingdom of Italy, untilItalian capitulation in September 1943, whereupon control passed to Germany. Izola was liberated by a naval unit fromKoper at the end of April 1945. After the end ofWorld War II, Izola was part of Zone B of the provisionally independentFree Territory of Trieste; after thede facto dissolution of the Free Territory in 1954 it was incorporated intoSlovenia, then a part ofYugoslavia.[5] The newly definedItalo-Yugoslav border saw the migration of many people from one side to the other. In Izola's case, many Italian speakers emigrated, and in their place Slovenian-speaking people from neighbouring villages settled in the town.[5]
In 1820, a thermal spring was discovered in Izola, leading to the town's earliest forms of tourism. Between 1902 and 1935 theParenzana, a narrow-gauge railway line, connected the town toTrieste andPoreč (known asParenzo until 1947).