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.
The townsite of Green River, Dakota Territory was platted by the Union Pacific Railroad in 1867. Although the Territory of Wyoming was created on July 25, 1868, the Town of Green River was incorporated on August 21,1868 under the laws of the previous Territory of Dakota since the laws of the Wyoming Territory had yet to be written. The Town of Green River was re-incorporated on June 10, 1891 under the laws of the State of Wyoming to remove any ambiguity.
The Union Pacific Railroad reached Green River on October 1, 1868 and was supposed to be the site of a division point for the railroad. Railroad officials were surprised to find that a town of 2000 residents and permanent adobe buildings had 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. 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. Bryan became the ghost town.