Nizhneudinsk is a town and the administrative center of Nizhneudinsky District of Irkutsk Oblast, Russia, located on the Uda River, 506 kilometers (314 mi) northwest of Irkutsk, the administrative center of the oblast. Population: 36,999 (2010 census); 39,624 (2002 census); 43,759 (1989 Soviet census); 39,700 (1970).