Definition

Traditional definitions of the Midwest include the Northwest Ordinance Old Northwest states and many states that were part of the Louisiana Purchase. The states of the Old Northwest are also known as Great Lakes states and are east-north central in the United States. The Ohio River runs along the southeastern section while the Mississippi River runs north to south near the center. Many of the Louisiana Purchase states in the west-north central United States, are also known as Great Plains states, where the Missouri River is a major waterway joining with the Mississippi. The Midwest lies north of the 36°30′ parallel that the 1820 Missouri Compromise established as the dividing line between future slave and non-slave states.^{[citation needed]}
The Midwest Region is defined by the U.S. Census Bureau as these 12 states:^[2]

• Illinois: Old Northwest, Mississippi River (Missouri River joins near the state border), Ohio River, and Great Lakes state.
• Indiana: Old Northwest, Ohio River, and Great Lakes state.
• Iowa: Louisiana Purchase, Mississippi River, and Missouri River state.
• Kansas: Louisiana Purchase, Great Plains, and Missouri River state.
• Michigan: Old Northwest and Great Lakes state.
• Minnesota: Old Northwest, Louisiana Purchase, Mississippi River, part of Red River Colony before 1818, Great Lakes state.
• Missouri: Louisiana Purchase, Mississippi River, Missouri River, and Border state.
• Nebraska: Louisiana Purchase, Great Plains, and Missouri River state.
• North Dakota: Louisiana Purchase, part of Red River Colony before 1818, Great Plains, and Missouri River state.
• Ohio: Old Northwest (Historic Connecticut Western Reserve), Ohio River, and Great Lakes state. The southeastern part of the state is part of northern Appalachia.
• South Dakota: Louisiana Purchase, Great Plains, and Missouri River state.
• Wisconsin: Old Northwest, Mississippi River, and Great Lakes state.

The Midwest Region of the National Park Service consists of these twelve states plus the state of Arkansas.^{[citation needed]}
The Council of State Governments, an organization for communication and coordination among state governments, includes in its Midwest regional office 11 states from the above list, omitting Missouri, which is in the CSG South region.^[13]