Yasothon is a town on the Chi River in the north-eastern region of Thailand. It is the capital and administrative center of Yasothon province and seat of its city district. In this district, subdistrict Nai Mueang incorporates the bounds of the town proper, which had a population of 21,134 in 2005. It lies 531 km (330 mi) north-east of Bangkok.

The Chi River is the longest river flowing wholly within Thailand. It is 765 kilometres (475 mi) long but carries less water than the second longest river, the Mun. The name of the river is "Mae Si" in the Isan and Lao languages of the region, being transliterated as "Chi" in Bangkok-Thai. In wet seasons there are often flash floods in the floodplain of the Chi River basin.