Karsun is an urban locality situated within the Karsunsky District of Ulyanovsk Oblast in Russia. It serves as a regional settlement with a population that has remained relatively stable over recent decades.
According to census data, the population was recorded at 7,936 during the 1989 Soviet census, increasing to 8,200 in 2002, and slightly decreasing to 7,748 by the 2010 census.