Nyssa is a city in Malheur County, Oregon, United States. The population was 3,267 at the 2010 census. The city is located along the Snake River on the Idaho border, in the region of far eastern Oregon known as the "Treasure Valley". It is part of the Ontario, OR–ID Micropolitan Statistical Area.

Malheur County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 31,571. Its county seat is Vale, and its largest city is Ontario. The county was named after the Malheur River, which runs through the county. The word "malheur" is French for misfortune or tragedy. Malheur County is included in the Ontario, Oregon Micropolitan Statistical Area, which is also included in the Boise Combined Statistical Area. It is included in the eight-county definition of Eastern Oregon.