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 Ri…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.