I think you are asking about a census.
A triennial event happens every three years.
An event that happens every other year is called a "biennial" event. This term is derived from the Latin "biennium," meaning "two years." Such events can include things like festivals, conferences, or exhibitions that occur once every two years.
I think you are asking about a census.
An event that occurs every 100 years is called a "centennial" event. The term "century" can also be used to describe this time span, and events that take place at this interval are often celebrated or noted for their significance. In some contexts, such as anniversaries, the term "centenary" is also appropriate.
Pre-, then add name of event.
Georgia winning a national championship in football.
An annual event
weekly
Annual.
Month
One's girlfriend.
A century.