Union is a city in Union County, Oregon, United States, originally platted in 1864, and located 15 miles (24 km) southeast of La Grande. It is the namesake of Union County, which references the Union states, or Northern States, of the American Civil War. The population was 2,152 at the 2020 census. The city is known for the numerous historic Victorian homes that line its Main Street, some of which are registered on the National Register of Historic Places. It is also home to Oregon State University's Eastern Oregon Agricultural Research Center, founded in 1888, which is contemporarily housed in the former Union train station.

Union County is one of the 36 counties in the U.S. state of Oregon, and one of the 8 counties of eastern Oregon. As of the 2020 census, the population was 26,196. The county comprises the La Grande micropolitan statistical area and the county seat is La Grande.