Corn is one of the principal crops of the 12 states composing the contiguous North Central Region of the United States. The "Corn Belt” includes all or parts of 11 of these states. It extends west to approximately the 25-inch rainfall line in eastern South Dakota, Nebraska, and Kansas, east to the Appalachian Mountains, and south to the Ohio River. It is by far the largest geographical area in the world in which corn is the primary economic crop.