The geographical features of Istria include the Učka/Monte Maggiore mountain range, which is the highest portion of the Ćićarija/Cicceria mountain range; the rivers Dragonja/Dragogna, Mirna/Quieto, Pazinčica, and Raša; and the Lim/Canale di Leme bay and valley. Istria lies in three countries: Croatia, Slovenia and Italy. By far the largest portion (90%) lies in Croatia. “Croatian Istria” is divided into two counties, the larger being Istria County in western Croatia. Important towns in Istria County include Pula/Pola, Poreč/Parenzo, Rovinj/Rovigno, Pazin/Pisino, Labin/Albona, Umag/Umago, Motovun/Montona, Buzet/Pinguente, and Buje/Buie. Smaller towns in Istria County include Višnjan/Visignano, Roč/Rozzo, and Hum/Colmo.

The northwestern part of Istria lies in Slovenia: it is known as Slovenian Istria, and includes the coastal municipalities of Piran/Pirano, Izola/Isola, and Koper/Capodistria. It also includes the Karstic municipality of Hrpelje-Kozina/Erpelle-Cosina.

Northwards of Slovenian Istria, there is a tiny portion of the peninsula that lies in Italy. This smallest portion of Istria consists of the comunes of Muggia/Milje and San Dorligo della Valle/Dolina with Santa Croce (Trieste) lying farthest to the north.

The ancient region of Histria extended over a much wider area, including the whole Karst Plateau with the southern edges of the Vipava Valley/Vipacco Valley, the southwestern portions of modern Inner Carniola with Postojna/Postumia and Ilirska Bistrica/Bisterza, and the Italian Province of Trieste, but not the Liburnian coast which was already part of Illyricum.