The Midwestern United States (in the U.S. generally referred to as the Midwest) is one of the four geographic regions within the United States of America used by the United States Census Bureau in its reporting.
The region consists of twelve states in the north-central United States: Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota and Wisconsin. A 2006 Census Bureau estimate put the population at 66,217,736. Both the geographic center of the contiguous U.S. and the population center of the U.S. are in the Midwest. The United States Census Bureau divides this region into the East North Central States (essentially the Great Lakes States) and the West North Central States.
Chicago is the largest city in the region, followed by Detroit, Indianapolis, Columbus, and Milwaukee. The Chicago-Joliet-Naperville, IL-IN-WI MSA is the largest metropolitan statistical area, followed by the Detroit-Warren-Livonia, MI MSA, the Minneapolis-St. Paul-Bloomington, MN-WI MSA, and the Greater St. Louis area. Sault Ste. Marie, Michigan is the oldest city in the region, having been founded by French missionaries and explorers in 1668.
The term Midwest has been in common use for over 100 years. A variant term, "Middle West", has been in use since the 19th century and remains relatively common. Another term sometimes applied to the same general region is "the heartland". Other designations for the region have fallen into disuse, such as the "Northwest" or "Old Northwest" (from "Northwest Territory") and "Mid-America". Since the book Middletown appeared in 1929, sociologists have often used Midwestern cities (and the Midwest generally) as "typical" of the entire nation. The region has a higher employment-to-population ratio (the percentage of employed people at least 16 years old) than the Northeast, the West, the South, or the Sun Belt states.
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". Many of the Louisiana Purchase states are also known as "Great Plains states".
While these states are for the most part relatively flat, consisting either of plains or of rolling and small hills, there is a measure of geographical variation. In particular, the eastern Midwest near the foothills of the Appalachian Mountains; the Great Lakes Basin; the Ozark Mountains of southern Missouri; the rugged topography of Southern Indiana and far Southern Illinois; and the Driftless Area of southwest Wisconsin, southeast Minnesota, and northeast Iowa exhibit a high degree of topographical variety. Prairies cover most of the states west of the Mississippi River with the exception of taiga-clad northern Minnesota. Illinois lies within an area called the "prairie peninsula", an eastward extension of prairies that borders deciduous forests to the north, east, and south. Rainfall decreases from east to west, resulting in different types of prairies, with the tallgrass prairie in the wetter eastern region, mixed-grass prairie in the central Great Plains, and shortgrass prairie towards the rain shadow of the Rockies. Today, these three prairie types largely correspond to the corn/soybean area, the wheat belt, and the western rangelands, respectively. Although hardwood forests in the northern Midwest were clear-cut in the late 19th century, they were replaced by new growth. Ohio and Michigan's forests are still growing. The majority of the Midwest can now be categorized as urbanized areas or pastoral agricultural areas.