Kotabaru Regency is one of the eleven regencies in the Indonesian province of South Kalimantan. It consists of two parts; the smaller but more populated part comprises Laut Island , the largest island off the coast of Kalimantan, together with the smaller Sebuku Island off Laut Island's east coast and even smaller islands nearby; the larger but less populated part consists of districts on the mainland of Kalimantan. The regency has an area of 9,442.46 km2, and had a population of 290,142 at the 2010 Census and 325,622 at the 2020 Census. The official estimate as at mid 2021 was 329,483. The regency seat is located at the large town of Kotabaru at the northern tip of Laut Island.