Hinterrhein District is an administrative district in the canton of Graubünden, Switzerland. It has an area of 617.67 km2 (238.48 sq mi) and has a population of 13,171 (as of 31 December 2014).Hinterrhein District consists of five Kreise (subdistricts) and twenty-four municipalities. This number decreased from thirty-two when the municipalities of Portein, Präz, Sarn, and Tartar merged on 1 January 2010 into Cazis.