Kotabaru Regency is one of eleven regencies located in the Indonesian province of South Kalimantan. It covers a total area of 9,354.93 km2 and is divided into two distinct geographical parts: an insular region and a mainland region. The regency seat is situated in the town of Kotabaru, which is located at the northern tip of Laut Island.
The smaller but more densely populated portion of the regency consists of Laut Island—the largest island off the coast of Kalimantan—along with Sebuku Island and several other nearby small islands. In contrast, the larger but less populated section comprises 12 districts on the mainland of Kalimantan. As of mid-2025, the total population of the regency was estimated at 336,785 residents.