Mexico claimed the Panhandle until 1836, when Texas claimed it.
Even though the land in Indian Territory was being divided and doled out in treaties, a formal survey had not been conducted. (To survey land is to make a detailed map of an area, including its boundaries and elevation.)
This caused confusion and overlapping boundaries. In 1831, Reverend Isaac McCoy was commissioned to survey the boundaries of the 7-million-acre Cherokee Nation as set out in the treaty of 1828.
McCoy, assisted by John Donelson and twenty men, spent the summer and fall surveying through the tangled brush and trees, over hills, and across streams.
The next year, McCoy surveyed the boundaries of the Seneca, Ottawa, and Shawnee reservations. John McCoy, Isaac’s son, surveyed the Cherokee Outlet in 1837.
Nathan Boone, son of frontiersman Daniel Boone, surveyed the boundary between the Creek and Cherokee Nations in 1833.
It was not until 1866 that all of the land in the Indian Territory, excluding the Panhandle, was surveyed.
The history of the Oklahoma Panhandle has its roots to the Compromise of 1850 and in 1845 when Texas became a state. The U.S. then acquired a vast amount of territory that Texas had claimed since its days as a Republic.
When Texas joined the Union as a slave state, it agreed not to extend its sovereignty over any territory north of 36 degrees and 30 seconds north. Therefore the northern boundary of the Texas Panhandle only stretched that far north, even though as a republic Texas claimed a strip of land stretching northward into modern Wyoming.
See Indiancountrynews.com's A story of the Oklahoma Panhandle to know more.