Planned in 1912 according to garden suburb principles by landscape architect Frederick Todd, a protege of Frederick Law Olmsted and designer of the Town of Mount Royal in Montreal, Leaside became the first town in Ontario to be comprehensively planned before construction. Although the Town of Leaside (later annexed by the Borough of East York in 1967) was incorporated in 1913, much residential construction did not proceed for almost a quarter-century, held back by the Depression and the Second World War.
Most of Leaside's residential development took place after the Leaside Viaduct was built across the Don Valley in 1927. The residential area was planned in concert with heavy industry, most of which has now been replaced by large-format retail. The study area boundaries exclude the industrial lands to the east and Mount Pleasant Cemetery to the south, but take in a residential area west of Bayview to Mount Pleasant. This area, historically part of the City of Toronto, was built out contemporaneously with Leaside.
Leaside is of moderate density, reflecting the fact that half of its dwelling stock is single-detached. Due to its integration with high-frequency transit service, transit accounts for about a quarter of all journeys to work and school.