The IRT Lexington Avenue Line is one of the lines of the A Division of the New York City Subway, stretching from Lower Manhattan north to 125th Street in East Harlem. The line is served by the 4, ​5, ​6, and <6> trains.

The 125th Street station is an express station with four tracks and two island platforms. It is the northernmost Manhattan station on the IRT Lexington Avenue Line of the New York City Subway. Located at Lexington Avenue and East 125th Street in East Harlem, it is served by the 4 and 6 trains at all times, the 5 train at all times except late nights, and the <6> train during weekdays in peak direction. This station was constructed as part of the Dual Contracts by the Interborough Rapid Transit Company and opened in 1918.