The South Side Elevated Railroad (originally Chicago and South Side Rapid Transit Railroad) was the first elevated rapid transit line in Chicago, Illinois. The line ran from downtown Chicago to Jackson Park, with branches to Englewood, Normal Park, Kenwood, and the . The first 3.6 miles (5.8 km) of the line opened on June 6, 1892, and much of its route is still used today as part of the Chicago "L" system.

The Chicago and South Side Rapid Transit Railroad Company was incorporated on January 4, 1888, and secured a franchise from the City of Chicago on March 26 of that year to construct an elevated railroad between Van Buren Street and 39th Street (Pershing Road). The franchise required the company to build along a right of way immediately adjacent and parallel to one of the alleys from Van Buren Street to 37th Street, rapidly earning the line the nickname of the "alley L". On April 2, 1892 the city authorized the extension of the line as far south as 71st street, and a further extension along 63rd Street was passed on April 7, 1893, the total cost of construction was estimated at $6,750,000.

A 6-car train carrying 300 guests made the inaugural run along first section of the line—running between a station at 39th Street and the Congress Terminal downtown—on May 27, 1892, and the line opened to the public ten days later. Initially the 3.6-mile (5.8 km) journey from 39th street to downtown took 14 minutes and cost 5¢. The line was gradually extended over the following months, with the route reaching Jackson Park on May 12, 1893 to provide service to the World's Columbian Exposition. Rolling stock on the line included 46 Forney-type (0-4-4) steam locomotives that were built at the Baldwin Locomotive Works in Philadelphia, and 180 46-foot (14.02 m)-long wooden passenger cars. The first 20 locomotives were delivered coupled into a single train in April 1892.

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