The earliest recorded Indian habitation of the area is traced back over 1000 years. The
Algonquins that lived in this area called the river Kichesippi "the Great River", and
called themselves Kichisippirini, the people of the Great River. The Algonquins mastered
travel on the river highways using birch bark canoes.
The "Ottawa" tribe of first nations, by the way, numbered about 8,000 and was centered near the mouth of the French River and on the large Islands in Lake Huron, but always considered Manitoulin Island as their original homeland. Ottawa comes from the Algonquin word "Adawe" meaning "to trade" and originates from their role as traders even before contact with Europeans.
French explorers came to the area in the early 1600s, following the lead of Etienne Brule who came up the Ottawa. He was accompanied by Jesuit missionaries who began attempting to convert the natives to Christianity. In 1613, Samuel de Champlain, the French commander of New France, himself visited the area for the purpose of trading for furs, and on June 4th 1613, he named one tributary on the southwest bank for the French word for curtain, "Rideau." In 1615, on a trip up the River he lost his astrolabe in a field near Cobden (west of Ottawa).
It was the French who named the Rideau River for the "curtain" of water as it flowed into the Ottawa River, and named the thundering Chaudière Falls. The French remained dominant in the area until after The American Revolution, which sent loyalist settlers north into Upper Canada, now Ontario. (it was called "upper" Canada because it was higher up the St Lawrence than Lower Canada, which is now Quebec).
More history of Ottawa