The Illinois Central Railroad (IC) was one of the earlier Class I railroads in the US. Its roots stretch back to abortive attempts by the Illinois General Assembly to charter a railroad linking the northern and southern parts of the state of Illinois. In 1850 U.S. President Millard Fillmore signed a land grant for the construction of the railroad, making the Illinois Central the first land-grant railroad in the United States.

The Illinois Central was officially chartered by the General Assembly in 1851. Upon its completion in 1856, the IC was the longest railroad in the world. Its main line went from Cairo, Illinois, at the southern tip of the state, to Galena, in the northwest corner. A branch line went from Centralia (named for the railroad) to the rapidly growing city of Chicago.

In 1876 the Illinois Central extended its track into Iowa. Throughout the 1870s, and 1880s the IC acquired and expanded railroads throughout the southern United States. IC lines crisscrossed the state of Mississippi and went as far as New Orleans, Louisiana to the south and Louisville, Kentucky in the east. In the 1880s, northern lines were built to Dodgeville, Wisconsin, Sioux Falls, South Dakota, and Omaha, Nebraska. Further expansion continued into the early twentieth century.

On August 10, 1972 the Illinois Central Railroad merged with the Gulf, Mobile and Ohio Railroad to form the Illinois Central Gulf Railroad. In the 1980s, the railroad spun off most of its east-west lines and many of its redundant north-south lines, including much of the former GM&O. Most of these lines were bought by other railroads, including entirely new railroads, such as the Chicago, Missouri and Western Railway and Chicago Central and Pacific Railroad. On February 29, 1988, the ICG dropped the "Gulf" from its name and again became known as the Illinois Central Railroad.