The riding covered the northern suburbs of the city of Toronto often including such towns as Aurora, Vaughan, Newmarket, Richmond Hill and Markham.

The British North America Act, 1867 designated the electoral districts to be used in elected the members of the House of Commons.

In 1952, it was defined as consisting of that part of the county of York lying north of Highway 7, excluding the town of Woodbridge.

In 1987, it was redefined to consist of the towns of Aurora, Richmond Hill and Vaughan, and the southern part of the Township of King.

In 1996, it was redefined to consist of the towns of East Gwillimbury, Georgina, and Newmarket, as well as the part of King north of Side Road 18, shedding a portion to create the new riding of Thornhill.