The earliest predecessor of the Chicago, Burlington and Quincy, the Aurora Branch Railroad, was chartered by act of the Illinois General Assembly on October 2, 1848. The charter was obtained by citizens of Aurora and Batavia, Illinois, who were concerned that the Galena and Chicago Union Railroad would bypass their towns in favor of West Chicago on its route; at the time, that was the only line running west from Chicago. The Aurora Branch was built from Aurora, through Batavia, to Turner Junction in what is now West Chicago. The line was built with old strap rail and minimal, if any, grading. Using a leased locomotive and cars, the Aurora Branch ran passenger and freight trains from Aurora to Chicago via its own line from Aurora to Turner Junction and one of the G&CU's two tracks east from there to Chicago. The G&CU required the Aurora Branch to turn over 70 percent of their revenue per ton-mile handled on that railroad; as a result, in the mid-1850s, surveys were ordered to determine the best route for a railroad line to Chicago.
The line from Aurora to Chicago was built through the fledgling towns of Naperville, Lisle, Downers Grove, Hinsdale, Berwyn, and the west side of Chicago. It was opened in 1864, and passenger and freight service began. Regular commuter train service started in 1864 and remains operational to this day, making it the oldest surviving regular passenger service in Chicago. Both the original Chicago line, and to a much lesser extent, the old Aurora Branch right of way, are still in regular use today by the Burlington's present successor BNSF Railway.