The oldest section of the line opened on May 31, 1900, running from the Loop to Wilson. It was constructed by the Northwestern Elevated Railroad. The route was extended to Central Street in Evanston on May 16, 1908, via leased and electrified trackage belonging to the Chicago, Milwaukee and St. Paul Railway. In November 1913, the North Side "L" was through routed with the South Side "L" lines through the Loop. The ground-level section between Leland Avenue and Howard Street was elevated on a concrete embankment structure and widened to four tracks in 1922.