This modest Post Office building debuted in June 1965 along Main Street in the Benton County community of Keystone. The building featured 688 square feet of interior floor space, and was rented by the U.S. Postal Service for $840 annually from a couple in West Union who constructed and owned the building. The previous Keystone Post Office had 621 square feet of space. Postal service was first established in Keystone on April 18, 1882, one year after the community was settled.