Housed in Green River, Wyoming's former federal post office, the Sweetwater County Historical Society Museum preserves and interprets the natural and cultural history of southwestern Wyoming. It contains thousands of artifacts, a large historical photograph collection, and local research materials. The museum's exhibits explore the state's history from millions of years ago to the present day. The building itself was placed on the National Register of Historic Places in 1997.
The post office was built in 1931 and designed by James Wetmore and Thomas Hyrum in the Classical Revival style. The need for a post office was recognized for years but it wasn't until the late 1920s that the project finally moved forward. The building was renovated to house the museum in 1967.