May 31, 1900 - service begins between downtown Loop and Wilson Avenue, using electric cars.
May 18, 1907 - service begins on Ravenswood branch between Belmont Avenue and Western Avenue.
December 14, 1907 - Ravenswood branch completed to Kimball Avenue, using ground level trackage west of Western Avenue.
May 16, 1908 - service extended north of Wilson Avenue to Central Street in Evanston, using trackage owned by Chicago Milwaukee and St. Paul Railway. CM&StP had previously operated steam powered commuter trains over this line, and continued to operate freight service. Line remained at ground level, and was electrified with overhead trolley wires. In subsequent years, the line was elevated on a ballasted embankment, completed in 1910 between Howard Street and University Place in Evanston, in 1916 between Wilson Avenue and Howard Street, and in 1928 between University Place and Isabella Street. The overhead electrification south of Howard Street would be replaced with third rail electrification after elevation of that segment.
November 17, 1908 - supplemental downtown terminal opened at North Water Street and Clark Street, relieving congestion around Loop elevated during rush hours.
April 1, 1912 - service extended north to Linden Avenue in Wilmette, over segment which would always remain at ground level.
August 6, 1919 - Chicago North Shore & Milwaukee Railroad interurban trains begin using line into downtown Chicago.
November 1, 1920 - Northwestern Elevated assumes responsibility for freight service, which had been operated by CM&StP. Two electric locomotives were used for the service, which was operated by CTA until 1973. Freight trains operated over the most westerly track between Wilson and Howard, and the east track between Howard and Foster. Gantlet tracks existed at stations north of Howard for platform clearance, and entire west track south of Howard was a gantlet for third rail clearance.
March 28, 1925 - Niles Center branch service begins, providing local service between Howard Street and Niles Center (now Skokie) over the Chicago North Shore & Milwaukee Railroad's new Skokie Valley route.