Assassin's Creed III's opening sequence is set in 1754.
The game begins with Haytham Kenway arriving in Boston and undertaking a mission connected to the Templars. This opening establishes the colonial setting and introduces several relationships before the story later shifts focus to his son, Connor Kenway.
The main historical narrative then moves through the American Revolution, including events in Boston, New York, and the frontier. The time span is important because the game deliberately presents the conflict through multiple perspectives rather than treating the revolution as a simple division between heroes and villains.
Players sometimes answer 1775 because that is a prominent year in the revolutionary portion of the story. However, the opening sequence predates the war's best-known outbreak and begins in 1754.