The IC is one of the early Class I railroads in the US. Its roots go 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 chartered by the Illinois General Assembly on February 10, 1851. Senator Stephen Douglas and President Abraham Lincoln were both Illinois Central men who lobbied for it. Douglas owned land near the terminal in Chicago. Lincoln was a lawyer for the railroad. 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 Chicago its tracks were laid along the shore of Lake Michigan and on an offshore causeway downtown, but landfilling and natural deposition have moved the present-day shore to the east.
In 1867 the Illinois Central extended its track into Iowa, and during the 1870s and 1880s the IC acquired and expanded railroads in 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.