Route 243 is a north/south highway on the south shore of the Saint Lawrence River. Its northern terminus is in Saint-Félix-de-Kingsey at the junction of Route 255 and its southern terminus is in the township of Potton where it crosses the Canada–US border at the North Troy–Highwater Border Crossing into Vermont and becomes Vermont Route 243. Route 243 is not a busy highway as it does not go through big towns. The highway has three concurrencies:

Municipalities along Route 243