The AYP drew participants from all over the world but the main exhibitors came from the United States and the State of Washington. New York, California, Idaho, and Utah contributed buildings as did four counties in Washington State—Yakima, King, Chehalis, and Spokane. The Exposition managers assigned sites for the buildings but did not have agreements beyond designating the location of the state buildings.
The California and Idaho Buildings followed a Spanish Mission style. The Utah Building was a replica of a section of a Hopi Pueblo, an adobe community dwelling built by the Bear and Snake families of the Hopi Indians. The Oregon Building followed a Roman classic style.
New York was the only state outside of the west to furnish a building and displays. This building was the site for many events and entertainments during the AYP, including receptions for the governor of New York and the French ambassador, and a luncheon for President Taft during his visit.
The New York Building was modeled after Auburn, William Seward's New York home. Since Seward was responsible for the purchase of Alaska—often called “Seward's folly” at the time—New York chose to honor him at the Exposition. A bronze statue of Seward, dedicated on Seward Day, September 10, 1909, stood in front of the New York building through the AYP, and was then moved to Volunteer Park where it stands today.
The four counties that contributed buildings, King, Spokane, Yakima, and Chehalis, all produced booklets and other materials to supplement their exhibits and help educate Exposition visitors about the opportunities in each county.
The King County Building was sponsored by the State of Washington. The main exhibit hall was devoted to a display of the county's agricultural and manufactured products, as well as mines, fisheries, and urban projects. One of the building's highlights was its replica of the Newcastle Mines in which visitors were sunk into the "mine" via a caged elevator. Another feature was the Denny Regrade illusion which demonstrated the ongoing construction project by allowing visitors to watch Denny Hill "disappear.
Items from other institutions: