Trains were so properly maintained at this location that railroaders recognized them by their "John Street polish".

[1] After the arrival of diesel locomotives, business slowed at the roundhouse, and the building was last used for its original purpose in 1986.

One-third of the original structure was dismantled, to allow construction of the Metro Toronto Convention Centre below, then reconstructed (1995) by Hotson Bakker Architects and is now home to Steam Whistle Brewing.

The remaining two-thirds was rehabilitated by IBI Group Architects and now house the Toronto Railway Museum and Cineplex's Rec Room entertainment complex.

Roundhouse Park with the restored wooden railway buildings, the turntable and courtyard was also completed by IBI and received design awards.

[3] The coaling tower and water tank are auxiliary structures still in the park from the working days of the John Street Roundhouse.

[5][6] The roundhouse and associated structures were first protected under Part IV of the Ontario Heritage Act, passed by Toronto City Council on August 12, 1996.

It was then designated under Part V of the act with by-law 634-2006 passed on July 27, 2006, as part of the Union Station Heritage Conservation District (encompassing the park, Union Station and the Royal York Hotel).