From the Wikipedia page [1]]
Irkutsk Oblast (Russian: Ирку́тская о́бласть, Irkutskaya oblast) is a federal subject of Russia (an oblast), located in southeastern Siberia in the basins of the Angara, Lena, and Nizhnyaya Tunguska Rivers. The administrative centre is the city of Irkutsk.
Irkutsk Oblast borders with the Republic of Buryatia and the Tuva Republic in the south and southwest, with Krasnoyarsk Krai in the west, with the Sakha Republic in the northeast, and with Zabaykalsky Krai in the east.