Sooners is the name given to settlers in the midwest of the United States who entered the Unassigned Lands in what is now the state of Oklahoma before President Grover Cleveland officially proclaimed them open to settlement on March 2, 1889 with the Indian Appropriations Act of 1889. The name derived from the "sooner clause" of the Act, which stated that anyone who entered and occupied the land prior to the opening time would be denied the right to claim land.
Sooners were often deputy marshals, land surveyors, railroad employees, and others who were able to legally enter the territory early. Some Sooners crossed into the territory illegally at night, and were originally called "moonshiners" because they had entered "by the light of the moon." These Sooners would hide in ditches at night and suddenly appear to stake their claim after the land run started, hours ahead of legal settlers.
The term Boomer relating to Oklahoma refers to participants in the "Boomer Movement," white settlers who believed the Unassigned Lands were public property and open to anyone for settlement, not just Indian tribes. Their reasoning came from a clause in the Homestead Act of 1862, which said that any settler could claim 160 acres (0.65 km2) of public land. Some Boomers entered and were removed more than once by the United States Army.
Those who actually observed the official start of the land run and began the race for free land often found choice sections of land already occupied by Sooners or, in some cases, by Boomers. Problems with Sooners continued with each successive land run; in an 1895 land run as much as half of the available land was taken by Sooners. Litigation between legitimate land-run participants and Sooners continued well into the 20th century, and eventually the United States Department of the Interior was given ultimate authority to settle the disputes.
In 1908, the University of Oklahoma adopted "Sooners" as the nickname of its football team, after having first tried "Rough Riders" and "Boomers". Eventually, Oklahoma became known as "The Sooner State."