Historic buildings in Markham, Ontario, reflect the area's long history of human activity, beginning with Indigenous communities such as the Huron-Wendat, Petun, Neutral, and Iroquois. Europeans began to build structures in Markham with the settlement of Thornhill and Unionville in 1794, and the establishment of Buttonville and Markham Village shortly afterwards during the early 19th century.
The oldest surviving building in the municipality dates back to 1800. Most of Markham's surviving historic buildings built before 1851 are residences still used for that purpose, though a small number of commercial and institutional buildings also remain.
Most historic structures and properties are presently registered with the Markham Register of Property of Cultural Heritage Value or Interest. A number of buildings and properties listed on the registry are protected under the Ontario Heritage Act. Buildings and structures in the registry are either listed as individual properties, or as a part of a larger heritage conservation district. The oldest structure listed on the registry is Philip Eckardt Log House, built in 1800.
The majority of Markham's oldest standing structures were built as private residences, many of which are still used for that purpose. However, some residences have been re-purposed for commercial use.
Historic buildings and structures are spread throughout Markham, although several historic buildings are clustered in four "heritage conservation districts," Buttonville, Markham Village, Thornhill, and Unionville. Developments in the heritage conservation districts is required to follow municipal guidelines laid out in the heritage district's conservation plan. These conservation plans were created to protect historic buildings, and to ensure that new developments within these districts complement the "character of the neighbourhood".
In addition to the heritage conservation districts, other clusters of heritage buildings are also situated at the Markham Museum and Markham Heritage Estates. The former is an open-air local history museum; while the latter serves as the city's "subdivision last resort", an area reserved for relocated heritage buildings that cannot be retained on their existing site. The museum and subdivision are both situated near the Markham Village heritage conservation district, although they do not form a part of said district.
The following is a list of the oldest buildings in Markham that are still erect, up to 1850, as listed by the Markham Register of Property of Cultural Heritage Value or Interest:
The following were notable buildings and structures that were erected in Markham by 1850, but were later demolished: