Corn is easily recognized, and is reported at Iowa sites more than any other crop. The cobs, including cupules and kernels (two to a cupule), are the most commonly preserved elements. Early dates on corn at Rainbow (13PM91) in Plymouth County, Cormorant (13MA387) in Marion County, Sweeting (13WS61) in Washington County, and Hadfield’s Cave (13JN3) in Jones County—probably represent Late Woodland contexts. No conclusive evidence exists in Iowa prior to A.D. 1000. Undisputed and abundant corn occurs at Great Oasis, Mill Creek, Glenwood, and Oneota sites.

Paleobotanists can identify several varieties of corn used in the Midwest based on the size of the cob, number of rows, and the size and shape of the kernels and cupules. Varieties include sweet, flour, flint, dent, and pop corn. Cupules preserved in archaeological sites can provide an idea of the size of the cob. The wider the cupules and the more closed, the larger sized the cobs.

Corn is what is called a C4 plant. During photosynthesis, all plants take up carbon in the form of CO₂. Some plants use a special enzyme to metabolize carbon into a molecule with four carbon atoms. Such plants are called C4 plants. Because they also metabolize almost all of a heavy form of carbon, (¹³C), C4 plants retain more ¹³C in their tissues. People who eat substantial quantities of these plants, or the animals that eat them, have more ¹³C in their bone collagen than those who do not. A study of bone chemistry from human skeletal remains can identify those populations who have added significant amounts of corn to their diet due to the high levels of ¹³C in their bone collagen. Dental health often declines in populations eating large quantities of corn due to its high sugar content.

Corn was, first and foremost, an important food plant, although cobs may also have been burned for fuel. Corn is high in carbohydrates with small amounts of protein and fat. Fresh ears of green corn were eaten boiled or roasted. Green and dried corn was also shelled, pounded, boiled, and made into corn cakes and bread. Varieties of dried corn were parched, roasted, and ground into meal or flour. Corn was also cooked with fat, meat, and other garden produce especially beans and squash. Boiled and parched corn was made into hominy. Dried—shelled and unshelled—corn was stored in woven bags and pits for overwinter, and kept as seed for the following season’s crop.

Corn smut was also eaten and used for medicine as were other parts of the plant including the stalk and pollen. Corn pollen had symbolic significance, and with other parts of the plant, was used in ceremony.

Many Late Prehistoric Iowa communities grew substantial amounts of corn and other garden crops on a grand scale creating acres of ridged gardens and fields of corn hills close to their settlements. At the Litka and Double Ditch Mill Creek sites in O’Brien County, remnants of such features still exist. Archaeologists uncover clues to the scale of prehistoric farming when they find specialized gardening and food processing implements and numerous subterranean cache pits used to store and protect garden surpluses. At the Wever Oneota site in Lee County, over 1500 such pits were uncovered.