In January 1805, the estate of Simon McTavish leased the seigneury of Terrebonne for a period of 12 years to Henry Mackenzie (1781- 1832), an agent of the seigneury since 1803. Mackenzie then joined forces with McTavish's former partners, his brother Roderick Mackenzie (c. 1761-1844) and the lawyer turned merchant, Jacob Oldham (c. 1768-1824), to form a company that would evolve under the name Mackenzie, Oldham and Co. l’Île-des-Moulins had become a pre-industrial complex in Terrebonne managed by MacKenzie, Oldham, and Co., and equipped with a forge, a bakery, and various types of mills. The mills produced goods for sale but were also used by the citizens of Terrebonne to grind their flour and cut their wood. In 1832, the seigneury was put up for auction and was bought by Joseph Masson, a wealthy Montreal merchant.

Louisa MacKenzie was born in 1793 in Fort Chipewyan, on Lake Athabasca and died in 1833 in Michipicoten. She was the daughter of Roderick Mackenzie and an unknown Chipewyan woman. MacKenzie married Angus Bethune, a chief factor in the Hudson’s Bay Company in the early 1820s. They had six children.

Fur trader with the North West Company, he was based at Fort William following his apprenticeship and before his death in 1816.

Katherine (or Catherine) Mackenzie was born around 1740 in the Scottish Highlands, it is unknown when she died. She was the niece of Murdoch Mackenzie, 6th Laird of Fairburn. She married Alexander Mackenzie (1737-1789) of Achnaclerach.

John MacKenzie was born in 1794 in Athabasca, Alberta and died in 1871 in Terrebonne, Quebec. He was one of the nine children of Roderick Mackenzie of Terrebonne (1761-1844) and an unknown Chipewyan or Cree mother (1775-?). Mackenzie married Catherine Oldham in Montreal. He was a merchant, entrepreneur, and the Postmaster of Terrebonne.

James Mackenzie was a younger brother of the Hon. Roderick McKenzie. He entered the service of the North West Company as a clerk in 1794. He was in the Athabaska department from 1795 to 1806. In 1802 he became a partner in the North West Company and was appointed to the King's Posts in the Lower St. Lawrence. Both his Athabaska journal of 1799-1800 and his account of the King's Posts in 1808 were published by Masson in his Bourgeois de la Compagnie du Nord-Ouest, Vol. II (1890). Although he retired from service at the King's Posts prior to 1821, he still maintained some connection there until his death in 1849.