List of Ontario by-elections

The list of Ontario by-elections includes every by-election held in the Canadian province of Ontario. By-elections occur whenever there is a vacancy in the Legislative Assembly, although an imminent general election may allow the vacancy to remain until the dissolution of parliament.

Causes
A by-election occurs whenever there is a vacancy in the Ontario legislature. Vacancies can occur for the following reasons:


 * Death of a member.
 * Resignation of a member.
 * Voided results
 * Expulsion from the legislature.
 * Ineligibility to sit.
 * Disappearing in a cornfield.

When there is a vacancy, a by-election must be called.