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. The boundaries of Unionville are not well-defined, as it is not a municipal entity, but several communities claim to be part of it.

However, Unionville was founded north of 16th in 1794, and many of the farms on and around Woodbine Ave. on its western edge considered themselves part of Unionville. The Unionville Ratepayers Association designated a relatively new road, Rodick Road, as its western boundary, in the 1980s. 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 about 80,000. Unionville is composed of many neighbourhoods including the historic centre of Unionville, Upper and South Unionville, Angus Glen, Cachet,Buttonville and Victoria Square. 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 Highway 407 is 2 km south on Kennedy Rd. The population lives in almost all parts of Unionville except for the south central industrialized area, which is now slated for massive intensification, under the name "Markham Centre". The railway line which links the area to Toronto via GO Transit Service ran to Coboconk (67 miles northeast) in 1872, with a 27-mile branch line from Whitchurch-Stouffville to Jackson's Point. It now only runs to Whitchurch-Stouffville. GO Transit took over passenger operations in 1982.

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 nine restaurants, including three pubs. Main Street (originally the laneway from the village's first grist mill) also has a number of "century homes" dating back to the 19th century. Each year, thousands of people 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 Gilmore Girls television show, and for other television and movie backdrops.

In the 1960s, major housing development came to Unionville and is still ongoing. Having old buildings available at low cost, a number of antique stores sprang up and for a while in the 1970s Unionville ranked high on the list of places to go to get antiques. After the commitment to a bypass was realised, in the 1970s, entrepreneurs appeared. The Old Country Inn opened for business and Old Firehall Sports brought a new clientele to the village. Over the next decades, the antique places disappeared being replaced by high-end antique and replica outlets, restaurants, pubs, and clothing establishments. Tourism was born. Starbucks appeared in the late 1990s. Many of the buildings have been spruced up, extended and upgraded to meet this new reality. The old original road, to the immediate east of Main Street, once considered to be swamp land, has been converted to a large parking lot.

Walking paths through the local conservation lands connect directly to the village roads, one of the most used being the path around Toogood Pond,[7] named after the Toogood family - the pond was originally the mill pond that powered the grist mill in the 1840s. In the early 20th century the pond was called Willow Pond or Willow Lake and was the home to several small summer cottages on north Main Street. Some had been cottages, for grist mill workers, in their earliest incarnation. Those cottages evolved into homes by the middle of the century, but are almost all gone now being replaced by large spacious expensive homes.

The Varley Art Gallery now stands at the north end of the commercial Main Street and is rapidly becoming a gallery of wide renown. It was started with the contributions of Mrs. McKay, who had supported Group of Seven artist Fred Varley for the later part of his life. Living in her home on Main Street Unionville, he did several paintings that are now part of the Art Gallery collection and the home is now part of the Art Gallery's holdings, being used for small art shows on a regular basis.

In the mid-1990s until the summer of 1999, Highway 407 was under construction. It is Ontario's first toll road and was first opened the summer of 1998 at McCowan Road. It was later extended to Brock Road.

The Unionville Arms, a well-known pub, burnt down on November 30, 2007. It had been in business for 19 years prior. The building itself was over a century old. The legendary building caught fire in the morning, supposedly due to a combination of faulty kitchenware and wiring, and the century-old insulation. The fire was put out three hours later. No one was hurt. The Arms reopened in very much its original appearance, towards the end of December 2008. Another popular pub is Jake's, housed in what used to be the funeral parlour.

A new library, the Markham Public Library (Unionville branch), was completed in 1984, replacing the older Unionville Library, which was renamed the "Old Library Community Centre", and is now used for dance classes, meetings, and a church. The new library occupies 14,000 sq. ft., and is based on a traditional village square surrounded by eight "houses" of books expressed on the exterior as postmodern Victorian dormers. The library, which contains approximately 100,000 books and audiovisual materials, was designed by architect Barton Myers.