Sayansk is a town located in the Irkutsk Oblast region of Russia. It is situated on the Oka River, approximately 270 kilometers (170 miles) northwest of the city of Irkutsk.
According to census data, the population of Sayansk has fluctuated over recent decades. The 2010 census recorded a population of 40,800, following a figure of 43,468 in 2002 and 38,169 during the 1989 Soviet census.