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 12,515 at the 2010 census.
Green River was incorporated in 1868 in what was then the Dakota Territory, on the banks of the Green River. The city was the starting point from which John Wesley Powell started his famous expeditions of the Green River, the Colorado River, and the Grand Canyon in the late 1800s. The town of Green River was originally supposed to be the site of a division point for the Union Pacific Railroad, but when the railroad finally reached the point, officials were surprised to find that the large town had already been established there, likely requiring costly negotiations for railroad land. They moved the division point 12 miles (19 km) west, creating the town of Bryan, on the Blacks Fork of the Green River.
At the time of its incorporation in 1868, Green River had about 2000 residents and permanent adobe buildings were being built. However, when the division point of the railroad was moved west, the settlement shrank to a mere 101 residents. Just when Green River was on the verge of becoming a ghost town, Blacks Fork dried up during a drought and the railroad was forced to move the division point back to Green River to ensure adequate water for its steam locomotives. The town was officially re-incorporated under the new laws of Wyoming on May 5, 1891, while Bryan became the ghost town.
The city is known as being one of the first in the United States to ban door-to-door solicitation, under the Green River Ordinance.
According to the United States Census Bureau, the city has a total area of 14.02 square miles (36.31 km2), of which, 13.73 square miles (35.56 km2) is land and 0.29 square miles (0.75 km2) is water.
Green River experiences a semi-arid climate (Köppen BSk) with long, cold, dry winters and hot, slightly wetter summers.