Oklahoma's 89er Day Celebration, also commonly known as the 89er Festival, is an annual April event commemorating Oklahoma's first land run, held on April 22, 1889, to open the Unassigned Lands of central Oklahoma to non-Indian settlement. The celebration occurs in various cities contained within the historic boundaries of the Unassigned Lands, a 1.8-million-acre geographic area that was bordered by the Cherokee Outlet on the north, the Chickasaw Nation to the south, the Cheyenne and Arapaho Reservation to the west, and the Shawnee, Sac and Fox, Iowa, Pawnee and Potawatomi reservations on the east.

The city of Guthrie, site of much of the Land Run's initial settlement and the territorial capital, held the inaugural 89er Day Celebration on the famous land opening's first anniversary. The ceremony, which continued in future years, received formal organization in 1911 when Guthrie citizens joined the town's chamber of commerce to host a parade and banquet. Past celebrations included lavish parades attended by thousands, as well as rodeos, horse races, and square dancing contests, along with the requisite 89er Day Queen crowning.

In 1935 the annual festivities received official sanction when the Oklahoma State Senate and House of Representatives authored Senate Concurrent Resolution Number 16, which provided for a "proper celebration" of the fiftieth anniversary of the opening of the Unassigned Lands for settlement. At the beginning of the twenty-first century Guthrie still annually held the state's largest observation of the historic event. Other cities also celebrated 89er day, including El Reno, Lexington, and Norman. The modern festival's activities typically center on a parade and offer carnival rides, historical reenactments, and old-time vendors and food.