Green Country, sometimes referred to as Northeast Oklahoma, is the northeastern portion of the U.S. state of Oklahoma, which lies west of the northern half of Arkansas, the southwestern corner the way of Missouri, and south of Kansas.

Oklahoma is a landlocked state in the South Central region of the United States. It borders Texas to the south and west, Kansas to the north, Missouri to the northeast, Arkansas to the east, New Mexico to the west, and Colorado to the northwest. Partially in the western extreme of the Upland South, it is the 20th-most extensive and the 28th-most populous of the 50 United States. Its residents are known as Oklahomans and its capital and largest city is Oklahoma City. The state's name is derived from the Choctaw words okla, 'people' and humma, which translates as 'red'. Oklahoma is also known informally by its nickname, "The Sooner State", in reference to the Sooners, settlers who staked their claims in formerly American Indian-owned lands until the Indian Appropriations Act of 1889 authorized the Land Rush of 1889 opening the land to white settlement.