When Louis Jolliet and Father Jacques Marquette arrived in Illinois country in 1673, they found a settler's paradise: fertile soil, sweeping prairies, forests, and water. A traversable network of rivers, easy low-land portages, and the accessibility of Lake Michigan combined to make the future state of Illinois easy to explore. In 1680 Robert Cavelier, sieur de La Salle, with a vision of the economic promise of the area, erected Fort Crevecoeur at the site of Peoria. Henri de Tonti, an Italian, accompanied La Salle. Two years later the two explorers built Fort St. Louis. By 1691, Tonti, who had taken over the settlement when La Salle left in 1685, moved Fort Louis eighty miles downstream. The new fort, known as Fort Pimitoui, included several buildings, Father Marquette's mission, and a village of fur traders' European-native families. Cahokia was settled by Seminarian priests in 1699, Kaskaskia by Jesuits four years later. Settlement followed at Fort de Chartres, Prairie du Rocher, St. Phillipe, and St. Genevieve.

In 1717 Illinois country was placed under the French government of Louisiana. France had ceded all possessions east of the Mississippi in 1763, although the British did not take possession, at Fort de Chartres, until two years later. From 1778-82 the present state of Illinois was a territory of Virginia and known as the county of Illinois. The American Revolution and the Treaty of Paris in 1783 extended the American boundary to the Mississippi, thus making the present Illinois part of the United States.
The establishment of the Northwest Territory in 1787 included Illinois land, but the area became part of the Indiana Territory in 1800. Nine years later the Illinois Territory was established, followed by statehood in 1818.

By 1800 the population of 2,000 included Americans from Virginia, Kentucky, Maryland, Tennessee, New York, New Jersey, Pennsylvania, and New England. In the spring of 1817 a group of English immigrants settled in Edwards County. Rhode Island farmers established a colony at Delavan, Tazewell County, in 1837. The states served as a conduit for the Underground Railroad before the Civil War.

Migration from Illinois was also significant and should not be overlooked by the genealogist. Kansas and Nebraska were the eventual homes of many Illinois settlers. The gold rush to California, the wagon trains of the Oregon Trail, and the open prairies of Iowa all tempted the populace of Illinois to venture further west.

When Europeans arrived in the Illinois country, the Illinewek or Illinois Indians were being dominated by the Iroquois of New York and were anxious to have the protection of a nearby fort or mission. In the Illinois valley region, they had once been the largest tribe, a loosely organized alliance of the Kaskaskia, Cahokia, Tamroa, Peoria, Michigamea, and Moingwena bands. Warfare and disease took their tolls, and by 1832 there were slightly more than two hundred of the tribe left in Illinois. The last land cession treaty in that year resulted in those few Native Americans being transferred to a Kansas reservation.

Included in the Illinois State Archives are the following: in Record Group 103.62, "Executive Section, Executive File," papers ca. 1824-32 concerning native Americans in Illinois (copies of treaties and speeches made by native Americans and government representatives at peace conferences, and depositions of Illinois citizens taken by state agents dealing with Indian depredations); and in Record Group 100, "Records of the Illinois Territory," there is material pertaining to speeches of, trade with, and treaties with Indians, and mention of the Cherokee, Delaware, Fox, Kickapoo, Osage, Ottawa, Potawatomi, Sauk, and Shawnee tribes.

Illinois has been the home of immigrants from many countries. Settlement patterns within the state frequently varied by nationality.

• Many German immigrants came to Illinois as affluent farmers, professionals, and artisans and were able to continue as such in America. There were also those who came with little or no money to spare. Immigrants came via the Great Lakes to Chicago. Working in the industries of the city, they could make good wages to buy their "American" farm. Unfortunately, living costs were high, savings grew slowly, and land values rose rapidly. The "farmer" often became a city dweller. One third of the foreign-born population in Illinois in 1850 was German. Religious, political, and economic factors had caused the massive migration. Cheap and fertile land in the Mississippi Valley brought them westward. Some of the earliest German settlements were in Dutch Hollow and Darmstadt, St. Clair County.
• The Irish immigrant may have stayed in the cities, employed as a day laborer or factory worker. They moved from place to place within the state, but by 1860 the nucleus of the Irish immigrant community was in Chicago. Many Irish worked on the construction of the Illinois and Michigan canal system. When this project was temporarily abandoned in the early 1840s, large numbers of Irish became farmers.
• There was considerable immigration from England, some of it prompted by the London Roman Catholic Emigration Society and the Mormon missionaries sent from Nauvoo by Joseph Smith. Kane County had a considerable Welsh population, and the lead mines brought the Cornish. In 1834 the Scottish began migrating to Illinois, their numbers in 1850 totalling 4,660.
• The first Norwegian settlement in the Midwest was founded by a group from New York in 1834 along the Fox River near Ottawa. Five-hundred Swedes established themselves at Bishop Hill in Henry County, and the Mormons settled at Nauvoo.
• Although there were scattered French-Canadians in Illinois country very early, there were few immigrants from France before 1830. Metamora in Woodford County was the first important French section, established in 1831, followed by several other French settlements. Bourbonnais, in Kankakee County, with a population of 1,719 in 1850, was a French-Canadian village that maintained Canadian customs for many years.
• Colonies of religiously-exiled Portuguese immigrants were located at Springfield and Jacksonville in 1849. There was a cluster of Bavarian Jews in Chicago. Although few Swiss immigrated to Illinois, there were settlements in St. Clair County, in Galena, and in Madison County-the most important center of Swiss population in Illinois.