The Rock Island District (RI) is a Metra commuter rail line from Chicago, Illinois, southwest to Joliet. Metra does not refer to its lines by color, but the timetable accents for the Rock Island District line are "Rocket Red" in honor of the Chicago, Rock Island and Pacific Railroad's Rocket passenger trains.

Metra is the primary commuter rail system in the Chicago metropolitan area serving the city of Chicago and its surrounding suburbs via the Union Pacific Railroad, BNSF Railway, and other railroads. The system operates 242 stations on 11 rail lines. It is the fourth busiest commuter rail system in the United States by ridership and the largest and busiest commuter rail system outside the New York City metropolitan area. In 2023, the system had a ridership of 31,894,900, or about 152,400 per weekday as of the fourth quarter of 2023. The estimated busiest day for Metra ridership occurred on November 4, 2016—the day of the Chicago Cubs 2016 World Series victory rally.