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 center is the city of Irkutsk. Population: 2,428,750 (2010 Census).

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.

The unique and world-famous Lake Baikal is located in the southeast of the region. It is drained by the Angara, which flows north across the province; the outflow rate is controlled by the Irkutsk Dam. The two other major dams on the Irkutsk Oblast's section of the Angara are at Bratsk and Ust-Ilimsk; both forming large reservoirs. The Lena has its source in Irkutsk Oblast as well, and flows north-east into the neighboring Sakha Republic.

Irkutsk Oblast consists mostly of the hills and broad valleys of the Central Siberian Plateau and of its eastern extension, the Patom Plateau.

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