The Ancaster incident was an attack on the Upper Canadian government official and politician George Rolph on June 3, 1826, in Ancaster, Upper Canada. Members of the Tory elite, motivated by suspected adultery and dislike of Rolph, dragged Rolph from his home and proceeded to tar and feather him. At the subsequent trials, government officials such as the solicitor general Henry John Boulton and the attorney general refused to prosecute the cases; instead, they recused themselves or acted as counsel for the accused. This led to several proceedings, in which Rolph was represented by his brother John Rolph, to determine which judges and court proceedings would be used for the trials. None of the defendants were criminally prosecuted, and Rolph received a verdict of £20 from two of the defendants; his appeal to increase the amount paid was unsuccessful.
Reformers, the political opponents of the Tories, cited the incident as evidence of the Tories engaging in political violence to maintain their power, contributing to the Reformers' victory in the 1828 elections for the Legislative Assembly of Upper Canada. The Gore county magistrates dismissed Rolph from his position as their clerk, leading to a legislative inquiry into the dismissal and Rolph's reinstatement to the role. John Walpole Willis, a judge in the civil lawsuit's appeal, admonished government officials for not pursuing criminal charges. This incident contributed to the legislative assembly investigating the abuse of power perpetuated by public prosecutors. Historians have cited the incident to highlight the tensions between the ruling elite and the growing agrarian society in Upper Canada, resulting in the Tories using violence in an attempt to retain their political and social influence within the province.