Farm country and onions in Ontario
Ontario sits in some of Oregon's most intensive farm country. This page sticks to what public sources say.
Western Treasure Valley
Wikipedia describes the irrigated fields in the northeast corner of Malheur County, known as the Western Treasure Valley, as the center of intensive and diversified farming. The county is 94 percent rangeland, and the Bureau of Land Management controls 72 percent of the land.
Onions
Oregon Agriculture in the Classroom reports that Oregon grew more than 1.5 billion pounds of onions in 2020, third most of any state, on close to 20,000 acres. It says most of Oregon's onions are grown on the east side of the state in Malheur, Morrow and Umatilla counties. It does not break out Malheur County's own share, and we have not found a current official county figure.
Oregon State University's Malheur Experiment Station, at 595 Onion Avenue in the Cairo area between Ontario, Vale and Nyssa, runs crop trials every year, and onions are among its work. OSU describes onions as a major crop in Malheur County and says visitors are welcome at the station.