It has been called Lake Ontario for 366 years, counting from when European records and maps permanently adopted the name.
- 366 Years (Since 1660): This is when French Jesuit historian Francis Creuxius first formalized the name Lacus Ontarius in written records. Mapmakers began standardizing the name on official regional maps shortly after.
- Centuries Prior: The exact total number of years is unknown because Indigenous nations, including the Wyandot and Haudenosaunee, used the name Ontarí'io for generations via oral tradition long before Europeans arrived.

