Originally the comté de Leinster, the comté de Lachenaie was established in the electoral reform of 1829. It was situated to the north-east of Montreal, about 35 kilometres from the town centre, at the junction of the rivière des Milles-Iles and the rivière des Prairies. The comté was partly located in the Basses-Terres of the St Lawrence, a region with very fertile soil and on the more rocky soil of the Canadian Shield. The area has good water supplies to irrigate fields. Though there were problems with navigation on the rivers because of their low flow of water, the rivers Assomption, Achigan and petite-Mascouche were used to transport timber and according to Bouchette in 1815 several flour and saw mills were located on them. The main timber produced in the area was maple, birch, beech and conifers such as pine.  The comté de Lachenaie was almost entirely divided into seigneuries though it contained several cantons such as Rawdon, Kilkenny and Kildare. In 1815, Bouchette identified the main seigneuries as Saint-Sulpice, Lachenaie, Repentigny and Assomption.
Since the first elections in 1792, the comté de Leinster had only elected one deputy with an English name: George McBeath. All the others were French-speaking and belonged to the Parti Canadien. For example, Joseph and Denis-Benjamin Viger were elected for the comté de Leinster and Ludger Duvernay for the comté de Lachenaie. When the comté de Lachenaie disappeared in 1841 following Union in favour of the comté de Leinster, Jacob DeWitt and Louis-Michel Viger were elected deputies. The main concentration of Patriote activity was in the north of the seigneurie de l’Assomption, between the seigneuries de Lachenaie and Saint-Sulpice, in the village of Saint-Roch-de-l’Achigan where several poorly documented assemblies took place between 1834 and 1837.
Although the habitants of Lachenaie were open to the reformist ideas of the Patriotes, few seem inclined to join the armed movement. In fact, only four individuals were implicated in the rebellions of 1837-1838 including Charles Courteau, a deputy. However, 84 individuals appear to have taken part in four Patriote activities. It appears that the intervention of the seigneur de Lachenaie, John Pangman and of the militia captain Étienne Mathieu was sufficient to prevent further problems.  Equally, there was no loyalist activity in the comté. After the union of the two provinces in 1841 and until Confederation in 1867, electors in the comté de Lachenaie tended to vote for reformers.
 Martel, Claude, Lachenaie 300 ans d’histoire à découvrir 1683-1983, (La Corporation du Tricentenaire de Lachenaie), 1983, pp. 22-24.
 Ibid, Bouchette, Joseph, Description topographique du Canada 1815, pp. 244-246.
 Ibid, Bouchette, Joseph, Description topographique du Canada 1815, pp. 226-231.
 DPQ, p. 483.
 DPQ, p. 770 on Joseph and pp. 768-769 on Denis-Benjamin
 DPQ, p. 227.
 DPQ, p. 770.
 Ibid, Martel, Claude, Lachenaie 300 ans d’histoire à découvrir 1683-1983, pp. 328-329.
 Ibid, Bernard, Jean-Paul, Assemblées publiques, résolutions et déclarations de 1837-1838, pp. 161-166 for the Patriote assembly on 29 July 1837 at l’Assomption.
 Ibid, Bernard, Jean-Paul, Rebellions de 1837-1838: Les Patriotes dans La Memoire Collective et Chez Les Historiens, pp. 309-310.
 Ibid, Martel, Claude, Lachenaie 300 ans d’histoire à découvrir 1683-1983, p. 329
 Ibid, Martel, Claude, Lachenaie 300 ans d’histoire à découvrir 1683-1983, pp. 27-28.