Nam Yuen is the southernmost district (amphoe) of Ubon Ratchathani Province, northeastern Thailand.
A group of people from Det Udom moved to Ban Chanla Na Dom of Champasak during the reign of King Mongkut. Later in 1881 the king of Champasak proposed to King Chulalongkorn to upgrade Ban Chanla Na Dom to Mueang Dom Pradit, under the control of the Champasak Kingdom. When Champasak became part of French Indochine, Mueang Dom Pradit was downgraded to be a tambon of Det Udom District. As the area of Det Udom was very large, the governor of Ubon Ratchathani proposed to the government to establish a minor district (king amphoe). This was created on 17 March 1969 by splitting off the four tambons: Song, Ta Kao, Yang, and Dom Pradit. It was upgraded to a full district on 29 March 1974.
The name Nam Yuen has two origins: at first the district office was in the area of the village Nam Yuen, and as well the area has three fertile rivers, Bon, Chong and Ta Em, as Nam Yuen in Thai means 'long-lasting water'.
Neighbouring districts are (from the west clockwise): Nam Khun, Det Udom, Na Chaluai of Ubon Ratchathani Province, Champasak of Laos and Preah Vihear of Cambodia. The Dom Yai River is an important water resource. The highest summits of the Phanom Dong Rak Range, including Phu Khi Suk (753 m), Phu Khok Yai (693 m), Phu Chep Thong (692 m), Phu Tangok (689 m) and Chong Bok (603 m) are in this district, in the area where the borders of Thailand, Laos, and Cambodia intersect.
The district is divided into seven sub-districts (tambons), which are further subdivided into 92 villages (mubans). Nam Yuen itself is a township (thesaban tambon) and covers parts of tambons Song and Si Wichian. There are a further seven tambon administrative organizations (TAO).

Source: https://en.wikipedia.org/wiki/Nam_Yuen_District