Just west of Hammond Gateway station, the route crosses into Illinois and Chicago city limits, at which point the track curves northwest, through the Hegewisch neighborhood and, after crossing the Bishop Ford Freeway and the Calumet River, converges with the Metra Electric line south of Kensington/115th Street station.

The South Shore Line then runs over the Metra Electric from Kensington/115th Street the rest of the way to Millennium Station.

[5] The CLS&SB leased the Kensington and Eastern Railroad on April 4, 1909, giving it access to Chicago.

That year the full line to Kensington on the Illinois Central was completed, and beginning on June 2, 1912, the electric cars were coupled to IC steam locomotives and run to downtown Chicago.

These locomotives had originally been constructed for the Soviet Union, but changing attitudes due to the Cold War prevented them from being delivered.

[10] On September 16, 1956, a street running section in East Chicago was removed with the building of a new alignment alongside the Indiana Toll Road.

[11] A truncation to west of downtown South Bend removed street trackage in that city from July 1, 1970.

[6] The Chesapeake and Ohio Railway acquired the CSS&SB on January 3, 1967 and continued the operation of passenger services.

[14] On July 5, 1994, NICTD closed the Ambridge, Kemil Road, Willard Avenue, LaLumiere, Rolling Prairie, and New Carlisle flag stops.

[15] The railroad began a 3-year project in 2009 to replace all catenary on its line between Michigan City and Gary, some of which was nearly 90 years old.

[16] The Chicago Region Environmental and Transportation Efficiency Program (CREATE), replaced a bridge on the South Shore Line across 130th Street, Torrence Avenue, and Norfolk Southern tracks in the Hegewisch neighborhood of Chicago as a part of a four-year project lasting from 2011 to 2015.

Targeted at business travelers, the train makes just two intermediate stops: Dune Park and East Chicago.

[26] In July 2009, NICTD announced its intention to relocate the Michigan City track south of its current location in order to smooth out the curves, cut down the number of grade crossings, increase speed and reduce maintenance costs.

The plan would require a demolition of residential and retail buildings currently located on the south side of 11th Street.

[28] The relocation effort faced a setback in March 2010 when NICTD announced that it was short necessary funds to complete the preliminary engineering study.

The preferred alternative identified by the study preserved an alignment similar to the current route but relocated the tracks alongside the street.

[38] Service on the remaining closed section between Gary and Dune Park restarted on April 9, 2024,[39][40] with a new schedule taking advantage of the double track beginning on May 14.

[34][42] NICTD planned to apply for federal funding for a preliminary engineering study and environmental survey of a Hammond-to-Lowell leg in 2009.

[49][50] The South Shore Line operates with a fleet of 82 rail cars built between 1982 and 2009 by Nippon Sharyo.

[54] An additional 26 cars are planned to be acquired, replacing those to be transferred to West Lake Corridor services.

[56] Pullman and the Standard Steel Car Company delivered electric multiple units to the CSS&SB between 1926 and 1929.

NICTD officials contend the shorter length of a Gary-to-Valparaiso run and the chance to use existing tracks there may make it a lower-cost alternative to the Munster-to-Valparaiso route.

In the 1980s and 1990s, there was some discussion about the possibility of extending the line from South Bend east to Elkhart County, Indiana.

[63][64] In 1988, Elkhart, Indiana Mayor James Perron pushed for the government to look into making long-term plans for an extension into his city.

On June 19, 1909, twelve people died when two trains collided head-on; one of the carriages involved in the incident was later preserved.

[73] Three passengers died on June 18, 1998, when a train ran into a truck that was trapped on the tracks near a Midwest Steel factory.