In 1973 and 1974, the Toronto Transit Commission (TTC) extended its YongeâÂÂUniversity subway line north from Eglinton station to four new stations along Yonge Street, with the line then terminating at Finch station. In mid-1961, the TTC had drawn up plans to extend the Yonge line to Steeles Avenue. These plans were kept secret and an extension to Sheppard Avenue was not approved until 1965. Construction was delayed by local opposition to the initially overground route through Hoggs Hollow, with Metro Toronto approving a route under Yonge instead. Construction started in 1968, with the line initially expected to open to Sheppard at the end of 1971. Completion was delayed multiple times due to labour disputes, a 1969 decision to extend the line farther to Finch Avenue, and poor soil conditions. A 1971 strike prompted the TTC to initially open the extension to while the section to Sheppard would open with the rest of the line to Finch.
The extension opened to York Mills in March 1973 and to Finch in March 1974. Due to a shortage of trains, half of rush-hour trains continued to terminate at Eglinton, though this was reduced the next year to exclusively occur in the morning. Short-turns at Eglinton would not be fully eliminated until 1979. In 1978, the Spadina subway extended the western leg of the line. In the 1990s, the two legs of the line were planned to be connected, forming a closed loop. However, in 2000, extensions were instead proposed to go farther north. Since then, the Yonge North subway extension (YNSE) has been proposed to extend the Yonge line north to near Highway 407 in Richmond Hill. Tunnelling on the YNSE is expected to begin in 2027 with no confirmed opening date as of 2025.
The Yonge subway line first opened on March 30, 1954, running between Union and Eglinton stations. The line was extended along University Avenue to Bloor Street in February 1963 as part of the BloorâÂÂUniversity subway project. The BloorâÂÂUniversity project also constructed the initial section of the BloorâÂÂDanforth line, which opened in February 1966.
In 1959, an extension of the Yonge line north to Finch Avenue was proposed to be built sometime after a line along the proposed Spadina Expressway was completed. In mid-1961, the TTC drew up a plan to extend the line to Steeles Avenue in two phases. However, when Alderman Willam Archer asked for the plan to be released, the executive committee of Metro Toronto voted to keep it secret.
In the 1960s, it was debated whether an extension on Yonge Street or one along Spadina should be implemented first, with supporters of a Spadina extension fearing overcrowding on the Yonge line if it were extended first. In 1964, a Yonge extension to Steeles was one of five projects being considered by Metro Toronto Council, along with the Spadina extension. In October 1965, Metro Toronto voted in favour of constructing a Yonge extension to Sheppard Avenue first, despite North York and the TTC supporting an extension farther north to Steeles Avenue.
Local opposition to the originally proposed route emerged in 1966. Near Hoggs Hollow, it was planned to be built above ground west of Yonge Street, but local ratepayers' associations preferred a route closer to Yonge and students of the local Loretto Abbey school were wary of its impact on the school's grounds. The TTC preferred the elevated route due to its lower estimated cost around $57 million, later adjusted to $67.8 million. In September 1966, Metro Toronto recommended a tunnelled route under Yonge Street in agreement with locals, despite this option costing $11.2 million more. The route was approved by Metro Toronto's executive committee and council in January 1967.
In February 1968, TTC board member Ford Brand proposed extending the line farther from Sheppard to Finch Avenue after the commission found it would cost $7 to $10 million to add parking at Sheppard. TTC chair Ralph Day supported this extension, with the additional parking to be built on lands owned by Ontario Hydro. In 1968, the cost of the further extension to Finch was expected to be $22million for a cut-and-cover option west of Yonge or $26million for a tunnelled option below Yonge. Despite promising to make a decision by August 15, 1968, Metro Toronto did not decide to extend the line to Finch until late 1969, after construction on the extension to Sheppard had started. The tunnel option was selected. The late decision-making delayed the project.
Four stations were built on the line, at , Sheppard, , and . These stations were farther apart than stations on other lines and local bus service would continue to run on Yonge Street after the extension was complete. An additional station was planned at Park Home Avenue during the extension's original design but was ultimately not built. A proposal to rough in the station to make it easier to build in the future was also rejected by Metro Toronto. The station was later built and opened in 1987 as North York Centre station. The tunnels were the first in the Toronto subway system to feature handrails for workers on the sides of tunnels. Additionally, four emergency exits were built due to the increased spacing between stations. One such exit would feature a horizontal tunnel to the nearby Don Valley Golf Course, designed that way to take advantage of the nearby slope down to the course and to prevent a climb to the surface along Yonge Street.
Construction of the project was originally expected to begin at the start of 1968, but the delayed completion of the BloorâÂÂDanforth line prevented the extension's construction from starting. Additionally, local opposition to the initially proposed route delayed the extension's approval by Metro Toronto. Construction began with the start of tunnelling in October 1968. In late 1969, the extension to Sheppard Avenue was expected to cost $79million and the cost of an additional extension to Finch had increased by $5million. At the time, Metro Toronto had agreed to fund all but $17million of the extension's cost, nearly half of which was to be covered by the Ontario government. It was expected to be complete around the end of 1971 despite labour disputes having disrupted work multiple times near York Mills, including at least one in 1968 due to safety concerns. Labour disputes delayed the project by around six months by 1971.
By January 1970, the extension to Sheppard was delayed again to late 1972, with the extension to Finch delayed to early 1974. Costs of the initial section to Sheppard increased by $21million due to a surge in labour costs and soil problems at two locations. TTC chair Ralph Day supported cut-and-cover construction over tunnelling the section from Sheppard to Finch to control cost. The decision to use cut-and-cover was credited with keeping costs under control. The portion to Sheppard was delayed again in May 1971 to the end of March 1973, with the final section to Finch opening a year later. Tunnelling was complete to just south of Highway 401 and construction had started on all stations except Finch. The cost of the section from Sheppard to Finch had increased to $37million by 1972. The section between York Mills and Sheppard was delayed again due to a labour dispute that had escalated to a strike by July 1971. In late 1971, while the strike was ongoing, the TTC approved initially opening the extension to York Mills, with Sheppard opening later. The strike was resolved in January 1972, but a separate months-long strike began immediately after, again delaying work.
The extension cost a total of $135million to build, less than the $140million estimated in 1970 but 20 percent higher than the $112million estimated for the whole extension in 1966. Additionally, 76 new subway cars were purchased for the extension in late 1969, costing $11.8million. Due to a shortage of subway cars when the extension opened, in early 1973, the TTC looked to extend its existing contract to an additional 88 subway cars to be used to relieve congestion on the existing network and to expand service both on the remainder of the extension to Finch as well as on the future Spadina branch of Line 1. The TTC placed an order for the 88 cars that May at a cost of $25.4million.
In 1972, a shortage of new subway cars prompted the TTC to recommend running only half of rush-hour trains on the extension once it opened to York Mills and to continue the practice once it had been extended to Finch. The first section of the extension to York Mills opened on March 31, 1973, with an opening ceremony held the day before. As suggested by the TTC, only half of rush-hour trains ran past Eglinton station, with headways of just over 4 minutes north of there compared to just over 2 minutes elsewhere on the line. All service at other times ran to York Mills. This arrangement led to confusion shortly after the section first opened. While there were fears of overcrowding on the Yonge line, excessive crowding did not occur as not many riders immediately began using the Yonge line following its extension. At the time, the remainder of the extension to Finch was reportedly 90 percent complete.
The remainder of the extension opened on March 30, 1974, with another opening ceremony held the day before. Service increased slightly to every four minutes north of Eglinton and every two minutes south of there, with peak-hour short turns at Eglinton continuing. Fears of overcrowding continued at the time, with the TTC proposing turning some trains back at Union station if necessary. On its first day of operation, crowding was noted and the 800-spot parking lot at Finch was full.
In May 1975, the TTC began running all afternoon trains to Finch, while maintaining short turns at Eglinton during the morning rush hour. The morning short-turns remained until June 1979, when the TTC started running all trains to Finch to reduce crowding north of Eglinton.
In January 1978, the Spadina subway extended the western leg of the line to Wilson station, which within two months appeared to be reducing crowding on the Yonge line. The rush-hour short turns remained until they were removed in 1979, with trains during the morning rush hour running either from Finch to or Wilson to Eglinton.
When the extension to Finch opened, North York mayor Mel Lastman hinted at supporting a further extension of the line north to Steeles Avenue, but such an extension would require approval of a newly-formed regional transportation authority. By 1993, the TTC instead proposed turning the YongeâÂÂUniversityâÂÂSpadina line into a closed loop, with the Yonge and Spadina lines connecting near Finch. This plan would later be revised to instead terminate at Steeles Avenue, which would allow service to York University. Later that year, Markham Mayor Frank Scarpitti instead proposed extending the Yonge line into York Region to near Highway 407. The loop proposal was abandoned by 2000, when the City of Toronto and York Region instead proposed an extension of the Spadina line into Vaughan.
By the end of 2009, an environmental assessment on the Yonge North Subway Extension (YNSE), which would extend the line to Richmond Hill near Highway 407, was completed. The YNSE project was revised in the early 2020s and tunnelling on the extension is expected to begin in 2027. As of December 2025, the opening date for the extension is unknown.