Kaskaskia, Illinois in the context of "American Bottom"

The Illinois Country (French: Pays des Illinois [pɛ.i dez‿i.li.nwa]; lit. 'land of the Illinois people'; Spanish: País de los ilinueses), also referred to as Upper Louisiana (French: Haute-Louisiane [ot.lwi.zjan]; Spanish: Alta Luisiana), was a vast region of New France claimed in the 1600s that later fell under Spanish and British control before becoming what is now part of the Midwestern United States. While the area claimed included the entire Upper Mississippi River watershed, French colonial settlement was concentrated along the Mississippi and Illinois Rivers in what is now the U.S. states of Illinois and Missouri, with outposts on the Wabash River in Indiana. Explored in 1673 from Green Bay to the Arkansas River by the Canadien expedition of Louis Jolliet and Jacques Marquette, the area was claimed by France. It was settled primarily from the Pays d'en Haut in the context of the fur trade, and in the establishment of missions from Canada by French Catholic religious orders. Over time, the fur trade took some French to the far reaches of the Rocky Mountains, especially along the branches of the broad Missouri River valley. The "Illinois" in the territory's name is a reference to the Illinois Confederation, a group of related Algonquian native peoples.

The Illinois Country was governed from the French province of Canada until 1717 when, by order of King Louis XV, it was annexed to the French province of Louisiana, becoming known as "Upper Louisiana". By the mid-18th century, major settlements included Cahokia, Kaskaskia, Chartres, Saint Philippe, and Prairie du Rocher, all on the east side of the Mississippi in present-day Illinois; and Ste. Genevieve across the river in what is now Missouri, as well as Fort Vincennes in what is now Indiana.

The Illinois campaign, also known as Clark's Northwestern campaign, was a series of engagements during the American Revolutionary War in which a small force of Virginia militia led by George Rogers Clark seized control of several British outposts in the region northwest of the Ohio River in what is now Illinois and Indiana. The campaign is the best-known action of the western theater of the war and the source of Clark's reputation as an early American military hero.

In July 1778, Clark and his men descended the Ohio River from the Falls of the Ohio, crossed overland to the Mississippi River and took control of Kaskaskia, Cahokia, and several other villages in British territory. Vincennes, on the Wabash River was occupied a few weeks later. The occupation was accomplished without firing a shot because many of the French-speaking inhabitants of the region were sympathetic to the Patriot cause. To counter Clark's advance, Henry Hamilton, the British lieutenant-governor based at Fort Detroit, reoccupied Vincennes with a small force in December 1778. In February 1779, Clark returned to Vincennes in a surprise winter expedition and retook the town, capturing Hamilton in the process. Virginia capitalized on Clark's success by establishing the region as Illinois County.The importance of the Illinois campaign has been the subject of much debate. Because the British ceded the entire area northwest of the Ohio River to the United States in the 1783 Treaty of Paris, some historians have credited Clark actions with nearly doubling the size of the original Thirteen Colonies. For this reason, Clark was acclaimed "Conqueror of the Northwest", and his Illinois campaign—particularly his surprise march on Vincennes—was greatly celebrated and romanticized.

Missouri French (French: français du Missouri) or Illinois Country French (French: français du Pays des Illinois) also known as français vincennois, français Cahok, and nicknamed "Paw-Paw French" often by individuals outside the community but not exclusively, is a variety of the French language spoken in the upper Mississippi River Valley in the Midwestern United States, particularly in eastern Missouri.

The language is one of the major varieties of French that developed in the United States. At one point it was widely spoken in areas of Bonne Terre, Valles Mines, Desloge, De Soto, Ste. Genevieve, Old Mines, Cadet, St. Louis, Richwoods, Prairie du Rocher, Cahokia, Kaskaskia, and Vincennes as well as several other locations. Speakers of Missouri French may call themselves "créoles", as they are descendants of colonial Louisiana French people of the Illinois Country (Upper Louisiana) and their native-born descendants.

George Rogers Clark (November 19, 1752 – February 13, 1818) was an American military officer and surveyor from Virginia who became the highest-ranking Patriot military officer on the northwestern frontier during the Revolutionary War. He served as leader of the Virginia militia in Kentucky (then part of Virginia) throughout much of the war. He is best known for his captures of Kaskaskia in 1778 and Vincennes in 1779 during the Illinois campaign, which greatly weakened British influence in the Northwest Territory (then part of the British Province of Quebec) and earned Clark the nickname of "Conqueror of the Old Northwest". The British ceded the entire Northwest Territory to the United States in the 1783 Treaty of Paris.

Clark's major military achievements occurred before his thirtieth birthday. Afterward, he led militia forces in the opening engagements of the Northwest Indian War, but was accused of being drunk on duty. He was disgraced and forced to resign, despite his demand for a formal investigation into the accusations. Clark left Kentucky to live in the Indiana Territory but was never fully reimbursed by the Virginian government for his wartime expenditures. During the final decades of his life, he worked to evade creditors and suffered living in increasing poverty and obscurity. He was involved in two failed attempts to open the Spanish-controlled Mississippi River to American traffic. Following a stroke and the amputation of his right leg, he became disabled. Clark was aided in his final years by family members, including his younger brother William, one of the leaders of the Lewis and Clark Expedition. He died of a stroke on February 13, 1818.

The siege of Fort Sackville, also known as the siege of Fort Vincennes or the Battle of Vincennes, was an American Revolutionary War frontier battle fought in present-day Vincennes, Indiana. In February 1779, an American militia led by Lieutenant Colonel George Rogers Clark defeated the British garrison of Fort Sackville commanded by Lieutenant Governor Henry Hamilton. Clark surprised the fort after a gruelling march from Kaskaskia, and following the execution of four Odawa captives, forced Hamilton's surrender.

Illinois County, Virginia, was a political and geographic region, part of the British Province of Quebec, claimed during the American Revolutionary War on July 4, 1778, by George Rogers Clark of the Virginia Militia as a result of the Illinois Campaign. Though part or all of the area was also claimed by Connecticut and Massachusetts, it was formally organized by the Commonwealth of Virginia later that year. The County was accorded official governmental existence, including legally defined boundaries and a formal governmental structure under the laws of the Commonwealth. The county seat was the old Illinois Country French village of Kaskaskia. John Todd was appointed by Governor Patrick Henry to head the county's government. The county was abolished in January 1782, and Virginia ceded the land to the new United States Confederation government in 1784. The area later became the Northwest Territory by an Act of Congress in 1787.

Geographically, the county was bordered to the southeast by the Ohio River, in the west by the Mississippi River, and in the north by the Great Lakes at the time of its existence. It included all of what were known as eastern Illinois Country under French sovereignty and Ohio Country. Politically, its effective reach extended only to the old French settlements of Vincennes, Cahokia, and Kaskaskia.

The Territory of Illinois was an organized incorporated territory of the United States that existed from March 1, 1809, until December 3, 1818, when the southern portion of the territory was admitted to the Union as the State of Illinois. Its capital was the former French village of Kaskaskia on the Mississippi River (which is still a part of the State of Illinois). The northern half of the territory, modern Wisconsin and parts of modern Minnesota and Michigan became part of the Territory of Michigan in 1818.

Randolph County is a county located in the U.S. state of Illinois. According to the 2020 census, it had a population of 30,163. Its county seat is Chester.

Owing to its role in the state's history, the county motto is "Where Illinois Began." It contains the historically important village of Kaskaskia, Illinois's first capital.