| Province: | QC |
| Type: | QC |
| Route: | 340 |
| Maint: | Transports Québec |
| Map: | Route 340-QC.png |
| Length Km: | 40.2 |
| Length Round: | 1 |
| Length Ref: | [1] |
| Direction A: | West |
| Direction B: | East |
| Terminus A: | County Road 18 at South Glengarry, Ontario |
| Terminus B: | in Vaudreuil-Dorion |
| Previous Type: | QC |
| Previous Route: | 339 |
| Next Type: | QC |
| Next Route: | 341 |
| Counties: | Vaudreuil-Soulanges |
| Junction: | in Saint-Telesphore in Saint-Clet in Vaudreuil-Dorion in Vaudreuil-Dorion |
Route 340 is a provincial highway situated in the Montérégie region of Quebec west of Montreal. It runs for just over 40 kilometers from the Ontario-Quebec border in Saint-Télesphore (as a continuation of Stormont, Dundas and Glengarry County Road 18) and ends in Vaudreuil-Dorion at the junction of Autoroute 20.
| RCM or ET | Municipality | Km | Junction | Notes | |
|---|---|---|---|---|---|
| Vaudreuil-Soulanges | Sainte-Télesphore | 0.0 | Ontario County Road 18 | WEST: to South Glengarry, Ontario | |
| 2.8 | 325 SOUTH: to Rivière-Beaudette 325 NORTH: to Sainte-Justine-de-Newton | ||||
| Saint-Polycarpe | 12.1 | Chemin Sainte-Catherine | SOUTH: to Saint-Zotique | ||
| 15.0 | Chemin Ranger | SOUTH: to Les Coteaux | |||
| Saint-Clet | 21.0 | 201 SOUTH: to Coteau-du-Lac 201 NORTH: to Hudson | |||
| Vaudreuil-Dorion | 34.3 | 342 SOUTH: to Vaudreuil-Dorion 342 NORTH: to Hudson | |||
| 34.8 35.2 | 30 SOUTH: to 30 NORTH: to | ||||
| 40.1 40.2 | 20 WEST: to Les Cèdres 20 EAST: to Pincourt | ||||