How did Oklahoma get its nickname?

Even before the land was thrown open to white settlement, many early settlers snuck across the border and made claims there. When the first official settlers were allowed across, they found these "sooners" already in possession of the land that they were hoping to take. This led to the state being called the Sooner State.
Oklahoma is known as the Sooner State. In the Land Run of 1889, land was available on a first come, first serve basis. People who broke the rules and attempted to acquire the land prior to the official start of the Land Run were called "Sooners". The name stuck.