The Chicago North Shore and Milwaukee Railroad (reporting mark CNSM), also known as the North Shore Line, was an interurban railroad that operated passenger and freight service over an 88.9-mile (143.1 km) route between the Chicago Loop and downtown Milwaukee, as well as an 8.6-mile (13.8 km) branch line between the villages of Lake Bluff and Mundelein, Illinois.

Operating examples of North Shore Line rolling stock have been preserved in railroad museums, and the former Dempster Street Station is listed on the National Register of Historic Places.

[6]: 5  Between 1938 and 1941, 4 miles (6.4 km) of the line through Glencoe and Winnetka were rebuilt as part of a Public Works Administration grade separation project which included the installation of automatic block signaling and overhead catenary along the improved section.

[5]: 3  The Skokie Valley Route was entirely double-tracked, located on private right-of-way, and utilized an automatic block signaling system.

[1]: 768–769  Power was supplied by a combination of third rail and overhead catenary, with the transition made between East Prairie Road and Crawford Avenue in Skokie.

[8]: 10 The Libertyville Division was a branch line which ran 8.6 miles (13.8 km) from Lake Bluff to Mundelein, parallel to Illinois Route 176.

[5]: Table 1 [14]: 62  Freight service was provided to a number of industries between North Chicago Junction and 10th Street, and deliveries of coal were transported from the Milwaukee Division to the Victory Memorial Hospital via the Glen Flora Avenue lines.

[7]: 187 [15]: 652  Connections existed with the city service of The Milwaukee Electric Railway and Light Company (TMER&L), which utilized the tracks on Wells Street between 2nd and 5th Avenues until it was discontinued in 1958.

[9]: 33  In 1920 a dedicated passenger terminal was constructed near the intersection of 6th and Michigan Streets, reducing interurban operations over the city line to 2.8 miles.

[16] When the North Shore Line assumed operations of the Chicago and Milwaukee Electric Railroad in 1916, trains only traveled as far south as Church Street in Evanston, where a passenger terminal and stub tracks had been constructed.

[7]: 114 In 1919, the North Shore Line negotiated a trackage rights agreement which permitted its trains to operate directly into Chicago over 12 miles (19 km) of the "L" from Howard Street to Roosevelt Road on the Near South Side.

[18]: 145–146  Power was supplied primarily by third rail, though overhead trolley wire was utilized on the outermost southbound track between Howard Street and Granville Avenue.

[4]: 79 In 1922, another trackage rights agreement was negotiated which permitted certain North Shore Line trains to operate over the South Side Elevated from Roosevelt Road to the 63rd/Dorchester station in the Woodlawn neighborhood.

[22]: 33, 45  In August 1899, through service began operating from downtown Waukegan to Church Street in Evanston, where passengers could transfer to trains of the Northwestern Elevated Railroad and continue into Chicago.

[23][22]: 45  The rudimentary, single-tracked interurban line was steadily upgraded over the following decade, with the addition of a second track, improvements to the physical plant and the gradual relocation from public roads onto private right-of-way where possible.

[22]: 83–85  Further construction proceeded at such a pace that trains began operating as far north as Kenosha, Wisconsin by December of that year, followed by Racine in September 1906.

[22]: 91  Shortly thereafter, the Panic of 1907 forced the Chicago and Milwaukee Electric into a prolonged period of insolvency, but in spite of ongoing financial trouble, construction in Wisconsin continued.

[22]: 158–159  The possibility of a direct entry into Chicago over the elevated lines was also studied during this time, with the intent to eliminate the necessity of transferring at Church Street, and thereby making the interurban service more competitive with the steam railroads.

The North Shore also created a network of motor coach (bus) lines to feed on potential traffic from territory not directly served by the company's trains.

An arrangement was made with the Chicago Rapid Transit Company, wherein local "L" service was begun over the new line to the Dempster Street station in Niles Center in 1925.

Though the Niles Center elevated service failed to prosper, the transit operator benefited from the construction of new shop facilities on vacant land along the southern part of the Skokie Valley line.

Initially after the stock market crash in 1929, business went on as usual, but as the depression deepened and as the Insull public utility empire began to crumble, the railroad entered receivership in 1932.

However, in 1937, President Franklin D. Roosevelt and his Secretary of the Interior, Harold L. Ickes (a Winnetka resident), announced a Public Works Administration program to "prime the pump" of the American economy.

Wartime earnings were high enough that the railroad's bankruptcy trustees were able to pay some of the company's outstanding debt and submit a reorganization plan.

When the franchise held by the North Shore subsidiary operating streetcar service in Waukegan expired in 1947, the company felt that a renewal was not justified.

The completion of the Edens Expressway through the Skokie Valley in late 1951 caused mounting ridership losses reflected on the railroad's earnings statements.

Though the abandonment proceedings garnered strong opposition in the communities affected, the railroad was successful in proving its case and was authorized to end service on the Shore Line.

[27] The report, released that October, revealed that passenger service had dropped to an average of 14,000 daily riders, and that the line was in dire need of modernization.

[28] This was prevented by the sale of the trackage between Dempster Street and Lake-Cook Road to the Chicago & North Western Railway for use as a freight line.

Abandoned and overgrown sections of track exist between Dempster Street and Lake Cook Road in the former Skokie Valley right of way.