Oklahoma was a state in the United States of America. In 1880, it was known as the Indian Territory. (COMIC: The Parliament of Fear)
In 2006, the First Doctor, Susan, Ian and Barbara visited during their tour of America. (PROSE: The Mother Road)
In 2011, in the wake of Miracle Day, an actual death was reported in Oklahoma, but turned out to be a fake. (TV: Dead of Night)
In the early 23rd century, Colonel White grew up in Oklahoma and had thought he'd never get out of there. (PROSE: Sleepy)