What term describes the 250th anniversary commemorated by America250?

The 250th anniversary commemorated by America250 is called a semiquincentennial.

The word combines roots meaning “half” and “five hundred,” so it denotes half of 500 years, or 250 years. It is the formal term used for the United States’ 2026 anniversary, although “America’s 250th anniversary” is more immediately familiar to many readers.

The term follows the naming pattern used for other milestone anniversaries. A centennial marks 100 years, a bicentennial marks 200 years, and a tricentennial marks 300 years. A sesquicentennial, by contrast, marks 150 years, so it is not the correct label for America250.

“Semiquincentennial” is sometimes misspelled or replaced by informal phrases such as “quarter-millennium.” In official discussions of the United States anniversary, however, semiquincentennial is the established name.