The Istrian Circle or Circle of Istria (German: Istrianer Kreis: Italian: Circolo d'Istria; Serbo-Croatian: Istarskog okružja) was a province of the Kingdom of Illyria from 1825 until 1849. It was formed by merging the circle of Trieste with the district of Pisino, thus reuniting most of the Istrian peninsula. In 1849 Illyria was reincorporated into the Austrian Empire and Istria returned to being a crownland (Kronland) of Austria as the March of Istria. The capital of the Istrian Circle was Pisino. The circle was divided into the following districts: Albona, Bellai, Buie, Capodistria, Cherso, Dignano, Lussino, Montona, Parenzo, Buzet, Pirano, Pisino, Rovigno, Pula, Veglia and Volosca.
Two antique castles, Albona/Labin and Fianona/Plomin which were two Agricultural Comunes, (municipalities during the Venice Republic under the control of the Podestá (Mayor/Magistrate). Each was subdivided into tvelve fractions called Districts/Contrade, by the Administrator of Dalmatia and Albania, Antonio Civran, as follows: Albona, Rippenda, S.Domenica/Sveta Nedelja, Istria, Dubrova, Vettua, Cere, Cugn, Bergod, Chermenizza, Vlakovo, Cerovica/Cerovizza. Later the District of Bersez, which included S.Martin was taken from the District of Volosca and added to the District of Albona.