Willowdale was first settled by Jacob Cummer (Jacob Kummer), who immigrated to Canada from the United States in 1797. Cummer was a mill owner on the nearby Don River, a proprietor of a tinsmith shop on Yonge Street and a self-trained doctor and veterinarian. Cummer was held in such high esteem by his neighbours they called the area "Kummer's Settlement". Cummer Avenue is named for Cummer.
David Gibson, a distinguished land surveyor, was another leader in this community. Like most of his neighbours, Gibson participated in the ill-fated Upper Canada Rebellion of 1837. He was thus charged with high treason and escaped to the United States, where he found employment as the First Assistant Engineer on the building of the Erie Canal.
Gibson returned to his Yonge Street farm in 1851, after being pardoned for his role in the Rebellion. He then helped to establish the "Willow Dale" post office, named after the many willow trees that once graced this district. Members of the Gibson family were still living in Gibson House in the 1920s when the residential subdivision of Willowdale began to take place.The Gibson House, built in 1851 in the Georgian Rival style, still stands in its original location at 5172 Yonge Street, and is now a historic house museum.