Iowa is a U.S. state in the Midwestern United States, a region sometimes called the "American Heartland". Iowa is bordered by the Mississippi River on the east and the Missouri River on the west; it is the only state whose eastern and western borders are formed entirely by rivers. Iowa is bordered by Wisconsin and Illinois to the east, Missouri to the south, Nebraska and South Dakota to the west, and Minnesota to the north.
Iowa is bordered by the Mississippi River on the east; the Missouri River and the Big Sioux River on the west; the northern boundary is a line along 43 degrees, 30 minutes north latitude. The southern border is the Des Moines River and a not-quite-straight line along approximately 40 degrees 35 minutes north, as decided by the
U.S. Supreme Court in
Missouri v. Iowa after a standoff between Missouri and Iowa known as the Honey War.
Iowa is the only state whose east and west borders are formed entirely by rivers.
Iowa has 99 counties, but 100 county seats because Lee County has two. The state capital, Des Moines, is located in Polk County.
Iowa's bedrock geology generally increases in age from west to east. In northwest Iowa, Cretaceous bedrock can be 74 million years old, in eastern Iowa Cambrian bedrock dates to ca. 500 million years ago.
Iowa is generally not flat; most of the state consists of rolling hills. Prior divides Iowa into eight landform based on glaciation, soils, topography, and river drainage. Loess hills lie along the western border of the state, some of which are several hundred feet thick. In the northeast, along the Mississippi River, is a section of the Driftless Zone, which in Iowa consists of steep hills and valleys which appear almost mountainous.
There are several natural lakes in the state, most notably Spirit Lake, West Okoboji Lake, and East Okoboji Lake in northwest Iowa (see Iowa Great Lakes). To the east lies Clear Lake. Man-made lakes include Lake Odessa, Saylorville Lake, Lake Red Rock, Coralville Lake, Lake MacBride, and Rathbun Lake. The northwest part of the state also contains a considerable number of remnants of the once common wetland areas such as Barringer Slough.
Iowa's natural vegetation is tallgrass prairie and savanna in upland areas, with dense forest and wetlands in flood plains and protected river valleys, and pothole wetlands in northern prairie areas. Most of Iowa is used for agriculture; crops cover 60% of the state, grasslands (mostly pasture and hay with some prairie and wetland) cover 30%, and forests cover 7%; urban areas and water cover another 1% each. The explosion in the number of high-density livestock facilities in Iowa has led to increased risk of rural water contamination and a perceived decline in air quality. Other factors negatively affecting Iowa's environment include the extensive use of older coal-fired power plants, fertilizer and pesticide runoff from crop production, and diminishment of the
Jordan Aquifer.
There is a dearth of natural areas in Iowa; less than 1% of the tallgrass prairie that once covered most of Iowa remains intact; only about 5% of the state's prairie pothole wetlands remain, and most of the original forest has been lost. Iowa ranks 49th of U.S. states in public land holdings. Threatened or endangered animals in Iowa include the Interior Least Tern, Piping Plover, Indiana Bat, Pallid Sturgeon, the Iowa Pleistocene Land Snail, Higgins' Eye Pearly Mussel, and the Topeka Shiner. Endangered or threatened plants include Western Prairie Fringed Orchid, Eastern Prairie Fringed Orchid, Mead's Milkweed, Prairie Bush Clover, and Northern Wild Monkshood.