The Chicago, Rock Island and Pacific Railroad (also known, variously, throughout its history as the "Rock Island Lines" and "The Rock") bears a crucial role in the history of American railroads, and particularly in the ways railroads influenced and transformed the settlement and development of the Midwest. CRIP was the first railroad to reach the state of Iowa, the first to actually lay track there, and the first railroad to throw a bridge across the Mississippi River. The road flourished throughout the Golden Age of Railroads, and managed to survive through most of a century in which the United States experienced increasing shrinkage of its rail presence. The railroad finally ceased operations, after numerous bankruptcies, in 1984.

A group of Iowa and Illinois civic leaders (including Colonel George Davenport, founder of the Iowa town that took his name) from what would later become the Quad Cities met in Davenport in June 1845 to discuss the founding of a railroad; ostensibly they wanted to provide an overland link between the Mississippi and Illinois Rivers with a railroad linking Rock Island to LaSalle, IL. They also hoped that a railroad would encourage settlement and development in the Rock Island-Davenport area. The group drew up a charter and on February 27, 1847 the Illinois legislature officially incorporated the Rock Island and LaSalle Rail Road Company.

Raising money proved difficult, and the new railroad was obliged to amend its charter to expand the route from Rock Island eastwards to Chicago. The amended charter was approved by the Illinois legislature on February 7, 1851, at which time the road's official name was changed to the Chicago and Rock Island Railroad. On October 1 of that year, construction of the road began on 22nd Street in South Chicago; the line made rapid progress and reached completion at Rock Island on February 22, 1854.

Meanwhile, across the Mississippi, the C&RI incorporated (in February 1853) a new road that would act as a western extension of its route: the Mississippi and Missouri Railroad. It began pushing west from Davenport along multiple lines westward across Iowa towards the Missouri River. The line was planned to run through Iowa City (a goal finally reached on the last day of 1855 after the town's citizens posted a $50,000 reward to the line builders if they could get a train into town by January 1, 1856; in freezing temperatures builders laid tracks and coaxed a stalled engine into the new depot just in time). However, duelling civic leaders from other towns persuaded the M&M to increase its lines, and the road agreed to split the line at Wilton Junction, with the main line continuing through Iowa City and the branching line going on to Muscatine. The latter was completed first, and on November 20, 1855 the first train ever to operate in Iowa travelled on the line from Davenport to Muscatine.

The C&RI had an historic moment in April 1856, when it completed the first bridge across the Mississippi River. The bridge was to be the key link between the C&RI and M&M routes. Despite (or perhaps because of) its importance, the bridge met with resistance from local steamboat companies. The issue reached a climax on May 6, 1856, when the steamboat Effie Afton crashed into the bridge piers while attempting to pass through the bridge; the boat burst into flames and destroyed part of the bridge. The shipowners sued the C&RI's Railroad Bridge Company, hoping to have the bridge declared a menace to river navigation; the bridge company was defended by Illinois lawyer Abraham Lincoln in the first trial. Lincoln argued that bridges across navigable rivers were of material benefit to the country. The jury failed to agree on a verdict and was discharged. The case eventually went to the U.S. Supreme Court, which declared in 1862 that the railroad had the right to bridge the river.

Construction by the M&M faltered, and the company went into debt (slow progress was a factor - it took M&M 6 years to lay track for a mere thirty miles from Iowa City to Marengo). To protect its land assets, the M&M sold itself to the more successful C&RI in July 1866. Under new incorporation in Iowa [and later in Illinois], the consolidated railroads became known as the Chicago, Rock Island and Pacific Railroad [CRIP], with John F. Tracy as its first president.

Over the course of the 19th century, CRIP, like a number of other American railroads, rapidly expanded through heavy construction as well as the acquisition of smaller roads. Over the course of its life, the road stretched across eleven states. Although its heaviest presence remained in Illinois and Iowa, especially on its original lines (Chicago to Rock Island, and Rock Island across the Mississippi to Davenport and then to Muscatine), CRIP also operated in Arkansas, Colorado, Kansas, Missouri, Nebraska, New Mexico, Oklahoma, South Dakota, and Texas. The road's major routes included: Minneapolis to Kansas City, MO (through Des Moines); St. Louis to Santa Rosa, New Mexico (through Kansas City); Herington, KS to Galveston, TX (via Dallas and Fort Worth); and Santa Rosa to Memphis, TN.

Of course, CRIP's extensive national presence made it a target for crime. In fact, the first successful train robbery in the American West was carried out against a Rock Island Express train on July 21, 1873. The James-Younger gang (led by infamous brothers Frank and Jesse James) derailed the train southwest of Adair, IA (killing the engineer in the process) and robbed it of nearly $3,000.

CRIP also operated extensive passenger service on many of its trains; operating jointly with the Southern Pacific Railroad, the Rock Island ran trains throughout much of the 20th century westward through the Rocky Mountains to California, Its Rocket Fleet ran passengers throughout the Midwest and into the West and Southwest.

The Chicago, Rock Island and Pacific Railroad, after a century of success and expansion, began its decline in the mid-20th century (along with most American railroads, as increased automobile and airplane traffic began to eat into railroad revenue and territory). In order to preserve itself and its assets, CRIP proposed to merge in 1964 with its still-mighty rival Union Pacific. However, protests by other railroads (who feared such a massive combination of roads), combined with the inevitable legal wranglings, slowed the process. By the time the prospective merger was approved in 1974, CRIP had lost much of its financial attractiveness to Union Pacific, which backed out of the merger. CRIP filed for bankruptcy (its third in its history), and despite plans to reorganize and restructure over the next few years, was ordered by a bankruptcy court in 1980 to shut down and liquidate its assets.

The railroad gradually sold off its facilities, engines, cars, and other assets, and the estate finally expired on June 1, 1984. The former railroad, now a mere shell company, was renamed the Chicago Pacific Corporation, and was eventually purchased by the Maytag Corporation, of Newton, IA, in 1988. This purchase brought the long history of this major Midwestern railroad to a final conclusion.