[nb 2] The battlefield was designated a National Historic Site of Canada in 1921 and is the last battle fought within the current boundaries of Ontario against a foreign invasion.

[6] The New York City-based Fenian Brotherhood was attempting to support related groups in Ireland to force the United Kingdom into negotiating toward the formation of an independent Irish Republic.

They took advantage of the ready supply of arms in the United States after the recently concluded Civil War, and of the ample number of unemployed young men who had emerged from that conflict with some degree of military training.

The plan was to take Canada temporarily hostage in the hope of demoralizing British rule in Ireland by precipitating a political crisis in Britain.

The Fenians had made little attempt at secrecy, and both American and British authorities were aware of the imminent military operation but could not pin-point the exact crossing points in advance.

The Fenian insurgents, led by Brigadier General John O'Neill, a former Union cavalry commander who had specialized in anti-guerrilla warfare in Ohio, secured boats and transferred some 800 men across the Niagara River, landing above Fort Erie, before dawn on June 1, 1866.

Starr's advance party rushed to seize the town, cut telegraph wires and take control of the railway yards south of Fort Erie by dawn as the rest of O'Neill's force was disembarking.

[10] U.S. authorities also allowed unarmed men to board the ferry from Buffalo and small boats freely crossed the Niagara River until the afternoon.

[11] Later during the night, O'Neill was reinforced by an additional column of 200 Fenians who had been deployed earlier on a bridgehead at Black Creek guarding against an approach from Chippawa in the north, bringing his total strength at Ridgeway to at least 650 men.

[1] A proclamation was posted explaining the reasons behind the invasion: “We come among you as the foes of British rule in Ireland, exiled from that native land of ours by the oppression of British aristocracy and legislation, our people hunted down to the emigrant ships, or worse, to that charnel of government institutions, the poor-house … We have taken up the sword to strike down the oppressor’s rod and deliver Ireland from the tyrant … We have no issue with the people of these provinces, and wish to have none but the most friendly relations … Our blows shall be directed only at the power of England …" .

The battle at Ridgeway was followed by a Fenian victory later in the afternoon over the heavily outnumbered Canadian volunteer Welland Field Battery (armed as an infantry unit) and the Dunnville Naval Brigade at Fort Erie.

Nevertheless, the rapid convergence of large British and Canadian reinforcements convinced many of the Fenians to return in haste to the United States – some on logs, on rafts, or by swimming.

Fewer than half of the Canadians on the field had practised firing live rounds before the day of the battle and there had been no military conflict in Canada since the Rebellions of 1837–38.

[18] One British soldier from the 47th Lancashire Regiment of Foot, Corporal Carrington, died from heat stroke on a forced march from Chippawa to Stevensville on the morning of the battle.

[22] In March 2012 a monument was unveiled in Tow Path Park, Buffalo, New York, near the site where the Irish troops assembled prior to the invasion.

[27] Colonel George Owen Starr, second-in-command Major John C. Canty (Fort Erie, Canada West), chief of staff/intelligence Lieutenant Rudolph Fitzpatrick, aide-de-camp.