The 'Sooner State' capital - Oklahoma City

Oklahoma City sprung up overnight - literally.

In 1889 it was a railroad stop with a population of 7 people.
When the Government announced they would be giving land in the Indian Territories away on a first come first served basis, the ensuing stampede of human traffic is what became refered to as the Land Rush, or Land Run.
The first Oklahoma Land Run took place at High Noon on April 22nd 1889. By then, the towns population had swelled from the original 7 to a tent city of over 10,000.
People who managed to stake a claim before the start of the land run became known as 'Boomers', and those who set out early on the official start date became known as 'Sooners' (originally a derogatory term meaning 'a cheat', it has since lost its negetive connotations).

Oklahoma didnt become a State of the Union until 1907 - its celebrating its centennial this year.