Irkutsk is the largest city and administrative center of Irkutsk Oblast, Russia. With a population of 587,891 as of the 2010 Census, Irkutsk i…Irkutsk is the largest city and administrative center of Irkutsk Oblast, Russia. With a population of 587,891 as of the 2010 Census, Irkutsk is the 25th-largest city in Russia by population, the fifth-largest in the Siberian Federal District, and one of the largest cities in Siberia.