The fertile land now known as the State of Iowa was first visited by primitive hunting bands of the Paleo-Indian period some 12,000 years ago. The first permanent settlers of the land were the Woodland Indians, who built villages in the forested areas along the Mississippi River, introduced agriculture, and left behind only their animal-shaped burial mounds.

Not until June 1673 did the first known white men come to the territory. When Louis Jolliet, accompanied by five French voyageurs and a Jesuit priest, Jacques Marquette, stopped briefly in Iowa on his voyage down the Mississippi, the region was uninhabited except for the Sioux in the west and a few outposts of Illinois and Iowa Indians in the east. Iowa was part of the vast, vaguely defined Louisiana Territory that extended from the Gulf of Mexico to the Canadian border and was ruled by the French until title was transferred to Spain in 1762. Napoleon took the territory back in 1800 and then promptly sold all of Louisiana Territory to the amazed American envoys who had come to Paris seeking only the purchase of New Orleans and the mouth of the Mississippi. After Iowa had thus come under US control in 1803, the Lewis and Clark expedition worked its way up the Missouri River to explore the land that President Thomas Jefferson had purchased so cheaply. Iowa looked as empty as it had to Jolliet 130 years earlier. The only white man who had come to explore its riches before the American annexation was an enterprising former French trapper, Julien Dubuque. Soon after the American Revolution, he had obtained from the Fox Indians the sole right to work the lead mines west of the Mississippi, and for 20 years Dubuque was the only white settler in Iowa.

The first wave of migrants into Iowa were the Winnebago, Sauk, and Fox, driven there by the US Army, which was clearing Wisconsin and Illinois of their Indian populations to make way for white farmers. Although President Andrew Jackson had intended that Louisiana Territory lying north of Missouri should forever be Indian land, the occupation of Iowa by the Indians was brief. Following the abortive attempt by an aging Sauk chieftain, Black Hawk, to win his lands in Illinois, the Sauk and Fox were driven westward in 1832 and forced to cede their lands in eastern Iowa to the incoming white settlers.

Placed under the territorial jurisdiction of Michigan in 1834, and then two years later under the newly created Territory of Wisconsin, Iowa became a separate territory in 1838. The first territorial governor, Robert Lucas, extended county boundaries and local government westward, planned for a new capital city to be located on the Iowa River, resisted Missouri's attempt to encroach on Iowa territory, and began planning for statehood by drawing boundary lines that included not only the present State of Iowa but also southern Minnesota up to present-day Minneapolis.

Because a new state seeking admission to the Union at that time could expect favorable action from Congress only if accompanied by a slave state, Iowa was designed to come into the Union with Florida as its slaveholding counterpart. A serious dispute over how large the state would be delayed Iowa's admission into the Union until 28 December 1846, but by the delay the people of Iowa got what they wanted—all the land between the Mississippi and Missouri rivers—even though they had to abandon Lucas's northern claim.

The settlement of Iowa was rapidly accomplished. With one-fourth of the nation's fertile topsoil located within its borders, Iowa was a powerful magnet that drew farmers by the thousands from Indiana, Ohio, and Tennessee, and even from faraway Virginia, the Carolinas, New York, and New England. Except for German and Irish immigrants along the eastern border and later Scandinavian immigrants during the 1870s and 1880s, Iowa was settled primarily by Anglo-American stock. The settlers were overwhelmingly Protestant in religion and remarkably homogeneous in ethnic and cultural backgrounds. Although New Englanders made up only 5% of Iowa's early population, they had a cultural influence that far exceeded their numbers. Many small Iowa towns—with their large frame houses, elm-lined streets, and Congregational churches—looked like New England villages faithfully replicated on the prairie.

Fiercely proud of its claim to be the first free state created out of the Louisiana Purchase, Iowa was an important center of abolitionist sentiment throughout the 1850s. The Underground Railroad for fugitive slaves from the South ran across the southern portion of Iowa to the Mississippi River. Radical abolitionist John Brown spent the winters of 1857 and 1859 in the small Quaker village of Springdale, preparing for his attack on the US arsenal at Harpers Ferry, in western Virginia.

Although the Democrats had a slight edge over their Whig opposition in the early years of statehood, a majority of Iowa voters in 1856 supported the new Republican Party and, for the most part, did so in succeeding years. A Republican legislative majority in 1857 scrapped the state's first constitution, which had been written by Jacksonian Democrats 12 years earlier. The new document moved the state capital from Iowa City westward to Des Moines, but it provided that the state university would remain forever in Iowa City.

When the Civil War came, Iowa overwhelmingly supported the Union cause. Iowans fought not only for their ideals, the abolition of slavery and the preservation of the Union, but also for the very practical objective of keeping open the Mississippi River, the main artery for transport of agricultural products.

In the decades following the Civil War, Iowans on the national scene, most notably US Senators James Harlan and his successor William B. Allison belonged to the conservative Republican camp, but they frequently faced liberal Republican and Populist opposition inside the state. The railroad had been lavishly welcomed by Iowans in the 1850s; by the 1870s, Iowa farmers were desperately trying to free themselves from the stranglehold of the rail lines. The National Grange was powerful enough in Iowa to put through the legislature the so-called Granger laws to regulate the railroads. At the turn of the century, as the aging Allison's hold on the state weakened, Iowa became a center for Republican progressivism.

Following World War I, the conservatives regained control of the Republican Party. They remained in control until, during the 1960s, new liberal leadership was forced on the party because of the debacle of Barry Goldwater's 1964 presidential campaign, controversy over US involvement in Vietnam, and effective opposition from a revitalized Democratic Party led by Harold Hughes. After Hughes gave up the governorship in 1969 to become a US senator, Republicans once more dominated the executive branch, but Democrats gained control of the state legislature and made strong inroads at the top levels of state government.

Iowa's economy suffered in the 1980s from a combination of high debt, high interest rates, numerous droughts, and low crop prices. Businesses left the state or automated, shrinking their work forces. The population dropped by 7.9%. By the 1990s the companies that had survived were in a much stronger position and diversification efforts in both the agricultural and manufacturing sectors had ushered in a period of cautious prosperity. The number of jobs in the service sector grew by 10%, and the state's unemployment rate in 1992 was 4.7%, substantially lower than the national average. By 1999 it had dropped to 2.5%, the lowest rate in the nation. In Iowa, as elsewhere in the Midwest, high-tech and service industries continued to pull workers away from farming—and away from the state, causing many to worry about a disappearing way of life. While the governor worked with state officials to entice young Iowans who had fled the state to return home, farming promised to be a hard sell for even the best marketers, as many of the state's agricultural producers eked by. By 2003, the US economy was slowly recovering from its 2001 recession, and Iowa was also feeling the effects. In July 2003, Iowa's unemployment rate was 4.6%, however, below the national average of 6.2%.

A debilitating drought hit Iowa in 1988, reducing corn and soybean harvests to their lowest levels in 14 years and prompting Governor Terry Branstad to declare a statewide emergency. In 1993, unusually heavy spring and summer rains produced record floods along the Mississippi River by mid-July. Countless levees, or earthen berms designed to raise the height of river banks, collapsed or were overrun. The entire state of Iowa was declared a disaster area. Altogether, it was estimated that 40 million acres of farmland were severely damaged and 500,000 acres permanently ruined. Agricultural woes continued to plague the state later in the decade. In 1999 Governor Tom Vilsack declared that Iowa was in a farm crisis, warning that problems plaguing the state's agricultural economy would soon affect urban and suburban areas. With the state's farmers getting record low prices for corn, soybeans, cattle, and hogs, producers were struggling to pay their loans.

In 1999 Governor Vilsack proposed one of the most dramatic increases in environmental spending in the state's recent history, asking for $10.5 million in new spending to improve the quality of Iowa's rivers and streams. He said the money was necessary to clean the state's waterways and boost recreation.

In 2001, the state took steps to allow refugees from other countries, including Afghanistan, to locate in small Iowa towns. Governor Vilsack during the early 2000s had established a record for promoting education, by signing into law over $200 million in new bills aimed at reducing class sizes. In 2003, he aimed to further improve education, health care, and the environment. Iowa House and Senate Republican leaders created an "Iowa Values Fund," a $503 economic development program, also supported by Vilsack.