Ontario is the largest city in Malheur County, Oregon, United States. It lies along the Snake River at the Idaho border. The population was 11,366 at the 2010 census. The city is the largest community in the region of far eastern Oregon, also known as the Western Treasure Valley.
Ontario is the principal city of the Ontario, OR-ID Micropolitan Statistical Area, which includes Malheur County in Oregon and Payette County in Idaho.
Ontario is approximately halfway between Portland and Salt Lake City. It is the closest city to the Idaho border along Interstate 84. The city's slogan is "Where Oregon Begins".
Ontario was founded on June 11, 1883, by developers William Morfitt, Mary Richardson, Daniel Smith, and James Virtue. In March 1884, Richard Welch started a post office for the quarter of Ontario, so named by James Virtue after Ontario, Canada.