Unionville is a suburban village in Markham, Ontario, Canada. It is located 33 km northeast of downtown Toronto and 4 km east of southern Richmond Hill. Unionville is located between Rodick Road as the western limit, McCowan Road as the eastern limit, Major MacKenzie Drive as the northern limit, Highway 407 as the southern limit. Main Street, which was Kennedy Road in the mid to late 20th century, runs through Unionville while the new Kennedy runs 300 m to the east.

The population of Unionville is presently about 30,000. Unionville is composed of many neighbourhoods including Olde Unionville, South Unionville, Angus Glen, and Berczy Village. Unionville is said to be one of the most affluent areas in the Greater Toronto Area with an average household income of $127,900. Rouge River runs north of the central part of Unionville and to the southeast. The highway (Highway 404) is to the west, the nearest interchange with the 407 ETR is 2 km south on Kennedy Rd. The population lives in almost all parts of Unionville except for the south central industrialized area. The railway line which links the area to Toronto via GO Train Service once ran as far as Lindsay, a town near Peterborough.

Tourism is a major part of Unionville’s economy. The historic village or downtown section of Unionville is typical of a small town that developed over a century or so starting in the early 1840s (when Ira White erected his Union Mills) through the middle to late 20th century. The historic Main Street Unionville attracts thousands of visitors each year — as of 2006 it boasted 9 restaurants, including 3 pubs. Main Street (originally the laneway from the village’s first grist mill) also has a number of "century homes" dating back to the 1800s. Each year, thousands visit Unionville during the Unionville Festival.

The main street has been used as a stand-in for fictional Connecticut town Stars Hollow during the first season of The WB’s (now The CW) Gilmore Girls television show, as well as other television and movie backdrops.

Most of the historic buildings in Unionville are included in List of historic buildings in Markham, Ontario.