The name "Toronto" comes from the Mohawk "tkoronto", a name for narrows between what is now Lake Simcoe and Lake Couchiching about 125 km north of Toronto. It means "trees that stand in water" and refers to an area used as a fishing weir for more than 4000 years.

The name migrated south as French explorers mapped the region, refering to what is now Lake Simcoe as "Lac Toronto", and giving that name as well to what is now the Humber River. The French built a fort at the mouth of the Humber River on the shore of Lake Ontario that is labelled on both French and English Maps as "Fort Toronto".

When the area was later settled by the British, John Graves Simcoe, the first Lieutenant Governor of Upper Canada disliked the native names and made the changes that are with us still today (Humber River, Lake Simcoe) and named the town here "York". The name was reverted back to the native "Toronto" in 1834 as anti-British sentiment grew in the colony and largely to avoid confusion with New York. It also helped shake the unflattering nickname "Muddy York." That, and nothing rude rhymes well with "Toronto".