The War of the Trillium is an annual SCA event held in Ealdormere on the Canada Day long weekend. Hosted by the Canton of Ardchreag the event has undergone many changes throughout its lifetime. Originally begun as Septentrian War Practice, it was changed to Ealdormere War Practice (or, as it was more normally called, EWP). In 2005, the event stewards maintained that the kingdom had had enough practice, and that it was time for the real deal. Originally envisioned as an annual “civil war”, the War of the Trillium, (also called the Trillium War or just “Trillies”) was born.

The event, named after the War of the Roses, is a camping event that usually lasts between four and five days. Usual activities include armoured combat, fencing, archery, thrown weapons, merchanting and bardic circles. House Galbraith celebrated its anniversary at Trillium and used to host a large party on the Saturday night of the event.

A theme for War of the Trillium is picked for each year, sometimes with energetic members of the kingdom's populace selected to act as leaders for each side. Mistress AElfwyn of Longwood, the Captain of the Early Period in 2005, was especially enthusiastic, making campaign posters plastered about the event site, singing slogans and actively campaigning for supporters.

The event was traditionally held at Heber Down Conservation Area in Whitby, Ontario, Canada, except for 2003 and 2004, when it had to move to nearby Orono due to booking conflicts. In 2013 it moved to the Eaglewood Campground in Pefferlaw, Ontario. In 2014 the event again moved to Orono where it has remained to the current day (2018).

• 1992, first Septentrian War Practice held
• 1999, event changes to Ealdormere War Practice
• 2005, event changes to War of the Trillium

• 2005, Early Period vs. Late Period
• 2006, Siege of Constantinople
• 2007, Normans vs. Saxons
• 2008, Ealdormerean Olympiad
• 2009, Baronies Unite!
• 2010, Ealdormerean Olympiad II
• 2011, Scottish Wars of Independence
• 2012, Pillage of the Damned
• 2013, Siege of Constantinople II
• 2014, No one Expects the Spanish Armada
• 2015, Ealdormere Royale: Crown, Coronet, and Two Smoking Barons
• 2016, Rebel Highland Games
• 2017, The Silk Road
• 2018, Laissez le Bon Temps Rouler! (Carnivale and Mardi Gras)
• 2019, A Monster among us - Beowulf & Grendel

Between 2003 and 2006, the canton published a broadsheet (newsletter) for the event. In the first year there were issues printed on three of the days of the event. In the following years there was only one issue produced per year.

The Annual Lord Ulrich von der See Memorial Ealdormerean Brewing Competition, held in memory of Lord Ulrich von der See, of both Ardchreag and Greenhithe, who passed away June 4, 2002. It has been held since A.S. 37 (2003) at Ealdormere War Practice (EWP), which later became the War of the Trillium.

Since becoming War of the Trillium the event has printed a t-shirt almost every year.

Trillium War is traditionally held Canada Day Weekend.