Green River is a city in and the county seat of Sweetwater County, Wyoming, United States, in the southwestern part of the state. The population was 11,825 at the 2020 census. It is the 7th most populous city in Wyoming.

Sweetwater County is a county in southwestern Wyoming, United States. As of the 2020 United States Census, the population was 42,272, making it the fourth-most populous county in Wyoming. Its county seat is Green River. By area, it is the largest county in Wyoming. Its southern boundary line abuts the north lines of the states of Colorado and Utah.