Illinois River in the context of Hennepin, Illinois

The Mississippi River System, also referred to as the Western Rivers, is a mostly riverine network of the United States which includes the Mississippi River and connecting waterways. The Mississippi River is the largest drainage basin in the United States. In the United States, the Mississippi drains about 41% of the country's rivers.

From the perspective of natural geography and hydrology, the system consists of the Mississippi River itself and its numerous natural tributaries and distributaries. The major tributaries are the Arkansas, Illinois, Missouri, Ohio and Red rivers. Given their flow volumes, major Ohio River tributaries like the Allegheny, Tennessee, and Wabash rivers are considered important tributaries to the Mississippi system. Before the Mississippi River reaches the Gulf of Mexico, it runs into its distributary, the Atchafalaya River.

Illinois (/ˌɪlɪˈnɔɪ/ IL-ih-NOY) is a state in the Midwestern region of the United States. It borders Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash and Ohio rivers to its south. Of the fifty U.S. states, Illinois has the fifth-largest gross domestic product (GDP), the sixth-largest population, and the 25th-most land area. Its capital city is Springfield in the center of the state, and the state's largest city is Chicago in the northeast.

Present-day Illinois was inhabited by Indigenous cultures for thousands of years. The French were the first Europeans to arrive, settling near the Mississippi and Illinois rivers in the 17th century Illinois Country, as part of their sprawling colony of New France. A century later, the revolutionary war Illinois campaign prefigured American involvement in the region. Following U.S. independence in 1783, which made the Mississippi River the national boundary, American settlers began arriving from Kentucky via the Ohio River. Illinois was soon part of the United States' oldest territory, the Northwest Territory, and in 1818 it achieved statehood. The Erie Canal brought increased commercial activity in the Great Lakes, and the invention of the self-scouring steel plow by Illinoisan John Deere turned the state's rich prairie into some of the world's most productive and valuable farmland, attracting immigrant farmers from Germany, Sweden and elsewhere. In the mid-19th century, the Illinois and Michigan Canal and a sprawling railroad network facilitated trade, commerce, and settlement, making the state a transportation hub for the nation, especially in the city of Chicago, which became the world's fastest growing city by the late 19th century. By 1900, the growth of industrial jobs in the northern cities and coal mining in the central and southern areas attracted immigrants from Eastern and Southern Europe. Illinois became one of America's most industrialized states and remains a major manufacturing center. The Great Migration from the South established a large Black community, particularly in Chicago, which became a leading cultural, economic, and population center; its metropolitan area, informally referred to as Chicagoland, holds about 65% of the state's 12.8 million residents.

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 Waterway system consists of 336 miles (541 km) of navigable water from the mouth of the Calumet River at Chicago to the mouth of the Illinois River at Grafton, Illinois. Based primarily on the Illinois River, it is a system of rivers, lakes, and canals that provide a commercial shipping connection from the Great Lakes to the Gulf of Mexico via the Illinois and Mississippi rivers.

The Illinois and Michigan Canal (I&M) opened in 1848. In 1900, the Chicago Sanitary and Ship Canal replaced the I&M and reversed the flow of the Chicago River so it no longer flowed into Lake Michigan. The United States Army Corps of Engineers maintains a 9-foot-deep (2.7 m) navigation channel in the waterway. The waterway's complex northern section is referred to in various contexts for study and management as the Chicago Area Waterway System (CAWS).

The Illinois and Michigan Canal connected the Great Lakes to the Mississippi River. In Illinois, it ran 96 miles (154 km) from the Chicago River in Bridgeport, Chicago to the Illinois River at LaSalle-Peru. The canal crossed the Chicago Portage, and helped establish Chicago as the transportation hub of the United States, before the railroad era. It was opened in 1848. Its function was partially replaced by the wider and deeper Chicago Sanitary and Ship Canal in 1900, and it ceased transportation operations with the completion of the Illinois Waterway in 1933.

Illinois and Michigan Canal Locks and Towpath, a collection of eight engineering structures and segments of the canal between Lockport and LaSalle-Peru, was designated a National Historic Landmark in 1964.

The Kankakee Torrent was a catastrophic flood that occurred about 19,000 calibrated years ago in the Midwestern United States. It resulted from a breach of moraines forming a large glacial lake fed by the melting of the Late Wisconsin Laurentide Ice Sheet. The point of origin of the flood was Lake Chicago. The landscape south of Chicago still shows the effects of the torrent, particularly at Kankakee River State Park and on the Illinois River at Starved Rock State Park.

Calhoun County is a county in the U.S. state of Illinois. As of the 2020 census, the population was 4,437, making it Illinois’ third-least populous county. Its county seat and biggest community is Hardin, with a population of 801. Its smallest incorporated community is Hamburg, with a population of 99. Calhoun County is at the tip of the peninsula formed by the courses of the Mississippi and Illinois rivers above their confluence and is almost completely surrounded by water. Calhoun County is sparsely populated; it has just five municipalities, all of them villages.

Calhoun County is part of the Metro-East portion of the St. Louis, MO-IL Metropolitan Statistical Area.

The French colonization of Texas started in 1685 when Robert Cavelier de La Salle intended to found the colony at the mouth of the Mississippi River, but inaccurate maps and navigational errors caused his ships to anchor instead 400 miles (640 km) to the west, off the coast of Texas. The colony survived until 1688. The present-day town of Inez is near the fort's site. The colony faced numerous difficulties during its brief existence, including Native American raids, epidemics, and harsh conditions. From that base, La Salle led several expeditions to find the Mississippi River. These did not succeed, but La Salle did explore much of the Rio Grande and parts of East Texas.

During one of his absences in 1686, the colony's last ship was wrecked, leaving the colonists unable to obtain resources from the French colonies of the Caribbean. As conditions deteriorated, La Salle realized the colony could survive only with help from the French settlements in Illinois Country to the north, along the Mississippi and Illinois rivers. La Salle's last expedition ended along the Brazos River in early 1687, when he and five of his men were murdered during a mutiny. Although a handful of men, led by Henri Joutel, reached Illinois Country, help never made it to the fort. Most of the remaining members of the colony were killed during a Karankawa raid in late 1688, though four children survived after being adopted as captives. Although the colony lasted only three years, it established France's claim to possession of the region that is now Texas. The United States later claimed, unsuccessfully, this region as part of the Louisiana Purchase because of the early French colony.

Grafton is the oldest city in Jersey County, Illinois, United States. It is located near the confluence of the Illinois and Mississippi Rivers. As of the 2020 census, the city had a total population of 626.

Grafton is a part of the Metro-East region and Greater St. Louis.