It consisted of two commuter railway lines to promote and service new suburban neighbourhoods outside of the then city limits.

Today, as part of a rails-to-trails project, the Beltline Trail lies on the right-of-way of the Don Loop.

At Yonge Street, it turned northwest travelling through Forest Hill until just north of Eglinton Avenue West.

The smaller Humber Loop headed west along the northwest rail corridor of the Grand Trunk Railway through Parkdale.

[2][3] A complete trip around the Humber Loop from and returning to Union Station was approximately 24 km (15 mi).

The Toronto Belt Land Corporation was incorporated on July 16, 1889, to subdivide and sell land in the new suburbs, and the Toronto Belt Line Railway Company was founded on March 23, 1889[5] to build a commuter railway to connect these new suburban areas to the city.

[6][7] A pamphlet by the Toronto Belt Land Corporation described the railway's mission as: "to economize time by rapid transit, and to carry men, women and children with comfort, safety and speed beyond the cramped and crowded city to the airy uplands; whence having enjoyed the rest and refreshment of commodious homes and spacious grounds, they can return on the morrow to renew, with quickened energies, the task of life."

[10] According to an August 1892 article in the Toronto Mail, the passenger coaches resembled an improved version of those used on the New York elevated railway at the time.

In 1906, the relatively short section in the Don Valley south of Winchester St. (across from Riverdale Park) was used as part of a new line by the Canadian Northern Railway connecting Toronto to Parry Sound.

[10] In 1910, the Grand Trunk Railway rebuilt the portion of the Don Loop between Fairbank Junction and Mount Pleasant Road for freight service to support the delivery of fuel and building supplies by rail for use in residential areas neighbouring the eastern end of the spur.

[9] The tracks on the steep grade (4%) in the Moore Park Ravine were pulled up during World War I because of a shortage of iron.

Three of the five 4-4-2T commuter tank locomotives that had been built especially for the Belt Line were eventually used on the Thousand Islands Railway in Gananoque, Ontario.

[15] The switch connecting the spur to the unloading siding was removed when the Mount Pleasant bridge over the Belt Line was rebuilt in 1976.

[1] Part of the right-of-way of the Don Loop was expropriated to build the Spadina Expressway, which terminated freight service east of Allen Road to Yonge Street in 1970.

A local citizen, Esther Carin, successfully lobbied city council to turn the section east of Allen Road into a walking trail.

The stations built for Belt Line passengers were of a standard design with two variations, large and small size.