The Chicago, Rock Island and Pacific Railroad (CRI&P RR) was a Class I railroad and was also known as the Rock Island Line, or, in its final years, “THE ROCK.” Its ancestor, the Chicago and Rock Island Railroad, was incorporated on February 7, 1851 and operated its first train on October 10, 1852, between Chicago and Rock Island, Illinois.

The Rock Island stretched across Arkansas, Colorado, Illinois, Iowa, Kansas, Missouri, Nebraska, New Mexico, Oklahoma and Texas. The easternmost reach of the system was Chicago. The system also reached Memphis, Tennessee, Denver, Colorado, and Santa Rosa, New Mexico. Southernmost reaches were to Galveston, Texas, and Eunice, Louisiana while in a northerly direction the Rock Island got as far as Minneapolis, Minnesota.

Major lines included Minneapolis to Kansas City, Missouri, via Des Moines, Iowa; St. Louis, Missouri, to Santa Rosa via Kansas City; Herington, Kansas, to Galveston, Texas, via Fort Worth, Texas, and Dallas, Texas; and Santa Rosa to Memphis. The heaviest traffic was on the Chicago-to-Rock Island and Rock Island-to-Muscatine lines.

The system got its start in Chicago and was a major player in the Iowa railroad industry.

The Rock Island jointly operated the Golden State Limited (Chicago—Kansas City—Tucumcari—El Paso—Los Angeles) with the Southern Pacific Railroad (SP) from 1902–1968. The name was shortened to the Golden State after 1948's modernization. Another joint venture with the SP, the Golden Rocket, was planned to enter service in 1948 but instead became "the train that never was," after SP withdrew from the joint train operating agreement. The Golden Rocket's uniquely-colored consist was placed in Golden State service instead.

The railroad operated a number of trains known as Rockets serving the Midwest, including the Rocky Mountain Rocket (Chicago—Omaha—Lincoln—Denver—Colorado Springs), the Corn Belt Rocket (Chicago—Des Moines—Omaha), the Twin Star Rocket (Minneapolis—St. Paul—Des Moines—Kansas City—Oklahoma City—Fort Worth—Dallas—Houston), the Zephyr Rocket (Minneapolis—St. Paul—Burlington—St. Louis) and the Choctaw Rocket (Memphis—Little Rock—Oklahoma City—Amarillo—Tucumcari).

The Rock Island did not join Amtrak on its formation in 1971, and continued to operate its own passenger trains. After concluding that the cost of joining would be the same as operating the two remaining intercity roundtrips (the Chicago-Peoria Peoria Rocket and the Chicago-Rock Island Quad Cities Rocket), the railroad decided to "perform a public service for the state of Illinois" and continue intercity passenger operations. Both trains were discontinued on December 31, 1978.

Once an acquisition target of the Union Pacific Railroad, Rock Island was victim to the longest and most complicated railroad merger proceedings in the history of the Interstate Commerce Commission. After a decade of hearings and studies, the ICC eventually approved the acquisition of Rock Island by Union Pacific, subject to many other conditions. Rock Island's track conditions had deteriorated greatly while merger proceedings were underway, and Union Pacific declined to pursue the merger plans.

In 1975, Rock Island entered receivership for its third and final bankruptcy. Attempts to reorganize failed, in part due to the US Department of Transportation reluctance to fund another railroad bailout like Penn Central-Conrail. In August 1979, the Brotherhood of Railway and Airline Clerks (BRAC) walked out on strike against the Rock Island in a dispute over retroactive wages. When no resolution of the strike seemed possible, the ICC ordered the Kansas City Terminal Railway to take over operations of the Rock Island in September 1979.

In mid-January 1980, the bankruptcy court ruled that the Rock Island could not be successfully reorganized and ordered its liquidation. Kansas City Terminal began the process of embargoing inbound shipments in late February, and Rock Island common carrier railroad operations ceased by March 31, 1980.

Segments of the Rock Island continued to be operated by other railroads, under ICC directed service orders, while Rock Island trustee William Gibbons began the process of selling or dismantling the railroad in what was the largest such liquidation in U.S. railroad history. Rock Island's holding company, the Chicago Pacific Corporation, continued on as its railroad/transportation subsidiary was liquidated.