This was my mother's maiden name, on the French canadian side of the family. The quebecois are very stubborn people, who refuse to lose their culture and language even though they are completely surrounded by english-speaking provinces. This surname stems from a family idiom, "lang" meaning "language" and "lois" meaning laws. "Keep the language, keep the laws". Americans typically pronounce it LAYNG-LOIS, but in French it is pronounced LAHNG LOO-AH.
Quite common in Quebec. Most of the Langlois are descended from pioneers Noel Langlois (1606-1684) and his first wife Francoise Grenier (1610-1665). A number of other unrelated French pioneers bore it too.