Ust-Ordyn-Buryat Autonomous Area, former administrative division, 9,000 sq mi (24,000 sq km), S Siberian Russia, in the Irkutsk region. Formed in 1937, it stretched from the Baykal Mts. to the Angara river. The capital was Ust-Ordynsk. Buryats, Buddhist descendants of the Mongols, made up 36% of the population; Russians most of the rest. Formed originally as a national area, it became an autonomous area in 1977. In 2008 the autonomous area was merged into the Irkutsk region.