Don Mills Station, located roughly under the intersection of Sheppard Avenue and Don Mills Road in North York, is the current eastern terminus of Line 4 Sheppard. Primary trip generators for Don Mills include Fairview Mall, and a large neighbourhood of condominium developments surrounding it. Don Mills also functions as a gateway to the northeastern areas of Toronto and Markham, for both bus passengers and motorists, featuring a commuter parking lot and a major bus terminal served by key TTC and Viva routes, located inside the fare paid area.
Don Mills typifies the design of Line 4 stations, with a platform and corridors that are spacious both horizontally and vertically. The station is organized on 4 levels, with 2 fare lines. The station's 3 entrances (all accessible) are at street level in headhouse buildings. The north entrance, accessed via the bus terminal, is adjacent to Fairview Mall and includes a small fare line. The east and south entrances stand opposite each other on the north and south sides of Sheppard Avenue, with the east entrance featuring a passenger pick-up and drop-off area.
Below the north entrance is the bus terminal; the terminal is situated on the northeast corner of the intersection, under a parking structure for Fairview Mall. Below the bus terminal and extending out under the street is the main concourse, to which the east and south entrances connect directly, via the main fare line. Below the main concourse is the platform level.
As with most other stations on Line 4, Don Mills features an island platform currently sized to hold a 4-car train, but with knockout panels allowing future expansion to 6-car trains. Don Mills has one knockout panel, at the east end of the platform. Typical terminal operations involve alternating westbound trains loading on either side of the platform, however one side can also be used to store a layover train without stopping operations. This is important because unusually for the Toronto subway, Don Mills was designed without full tail tracks; short tail tracks do exist east of the station as a by-product of the knockout panel shortening the platform, but are too short to hold a full train.