Arock is an unincorporated community in Malheur County, Oregon, United States. It is part of the Ontario, OR–ID Micropolitan Statistical Area. Arock is three miles (5 km) north of U.S. Route 95 between Jordan Valley and Rome. Arock was supposedly named in 1922 for a large rock bearing Native American petroglyphs in the vicinity. Arock post office was established in 1926. Its ZIP Code is 97902. The oldest building in Malheur County, Sheep Ranch Fort, is near Arock. It was added to the National Register of Historic Places in 1974. Arock is one of several places in southeast Oregon that were settled by Basque herders.