Roi Et is one of Thailand's seventy-six provinces lies in central northeastern Thailand also called Isan. Neighboring provinces are Kalasin, Mukdahan, Yasothon, Sisaket, Surin, and Maha Sarakham.

The Chi River is the longest river flowing wholly within Thailand. It is 765 kilometres long but carries less water than the second longest river, the Mun. The name of the river is "Mae Si" in the Isa