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.

The Powell Geographic Expedition of 1869, led by American naturalist John Wesley Powell, was the first thorough cartographic and scientific investigation of long segments of the Green and Colorado rivers in the southwestern United States, including the first recorded passage of white men through the entirety of the Grand Canyon. The expedition, which lasted approximately three months during the summer of 1869, embarked from Green River Station, Wyoming Territory and traveled downstream through parts of the present-day states of Colorado and Utah before reaching the confluence of the Colorado and Virgin rivers in present-day Arizona and Nevada. Despite a series of hardships, including losses of boats and supplies, near-drownings, and the eventual departures of several crew members, the voyage produced the first detailed descriptions of much of the previously unexplored canyon country of the Colorado Plateau.