Kostanjica is located in the municipality Grožnjan, in Istra County at an elevation of 109 meters above sea level and it covers the area of 3.82 km² (1.47 sq. miles). According to the 2011 census report, there were 48 inhabitants. It is largely populated by Italians (87%), but also Croats (13%). Nearby places: Završje, Antonci, Žudetići, Trombal, Mastelići, Vižintini Vrhi, Vrbani, Grožnjan, Makovci and Bijele Zemlje.