What formal term describes the 250th anniversary celebrated by the United States Semiquincentennial?

The formal term for the 250th anniversary celebrated by the United States Semiquincentennial is “semiquincentennial.”

The word combines Latin- and Greek-derived numerical elements: “semi” means half, while “quincentennial” relates to 500 years. Half of 500 is 250, so the term describes a 250-year anniversary.

The name can seem confusing because “bi” in bicentennial refers to two centuries, or 200 years, not to two times 100 in a broader anniversary sequence. A tricentennial marks 300 years, while a sesquicentennial marks 150 years.

America250 is the shorter campaign name used for the observance. Other historical alternatives sometimes appear, including sestercentennial and quarter millennium, but semiquincentennial is the formal name used for the United States’ 2026 anniversary.