The United States will celebrate its Tricentennial in 2076, 50 years after America250.
A tricentennial marks 300 years. Since the Declaration of Independence was adopted in 1776, adding 300 years produces 2076. That anniversary will follow the 1976 Bicentennial and the 2026 Semiquincentennial in the sequence of major national milestones.
The 2076 date is a mathematical consequence of the 1776 independence milestone, not a claim that the present constitutional system began that year. The Constitution was adopted in 1787, and the federal government under it began operating in 1789.
Future anniversary names can be confusing because “tri” refers to three centuries, while “semiquin” in semiquincentennial refers to half of five centuries. Both labels describe elapsed time from the 1776 Declaration.