Sergelen is a sum of Dornod Province in eastern Mongolia. In 2009, its population was 2,198. Khogne District, founded in 1931, and Kherlen…Sergelen is a sum of Dornod Province in eastern Mongolia. In 2009, its population was 2,198. Khogne District, founded in 1931, and Kherlenbayan District, founded in 1946, were merged in 1961 to form Sergelen District, centered on the slopes of Sergelen Kharat Mountain.