Udayapur District (Nepali: उदयपुर जिल्ला, is one of the 14 districts of Koshi Province in eastern Nepal. The district, with Triyuga as its district headquarters, covers an area of 2,063 km2 and in 2001 had a population of 287,689, in 2011 of 317,532, in 2021 of 342,773