The North Central Service (NCS) is a Metra commuter rail line running from Union Station in downtown Chicago through northwestern and far northern suburbs to Antioch, Illinois. In December 2022, the public timetable shows seven weekday departures from Chicago. This line does not run at all on weekends or holidays. While Metra does not explicitly refer to any of its eleven routes by colors, the NCS' timetable accents are lavender, a shade of purple. It is one of two Metra lines that do not have a specific color for a fallen flag railroad that used to operate on the route.

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.