March 2, 1819
The 100th meridian described in the Adams-Onis Transcontinental Treaty became the western boundary of the new Arkansas Territory. The western half of the original Arkansas Territory was soon to become Indian Territory. An uproar arose in Arkansas in 1820 when a swath of territory between the Arkansas and the Red rivers, said to be populated by 3,000 whites, was assigned by treaty to the Choctaw Indians. Disputes over the western border of Arkansas continued until 1886, when the current boundary was settled.