Renfrew, Ontario is sometimes cited as the birthplace of the NHL because it was the location of a meeting in 1909 that led to the formation of the precursor to the NHL, the National Hockey Association (NHA), which later evolved into the NHL.
At the time, the NHA was composed of teams from Ontario and Quebec, including the Montreal Canadiens, Ottawa Senators, and Toronto Arenas, among others. In 1917, the NHA was reorganized and renamed the NHL, with its headquarters in Montreal, Quebec.
So while the formation of the NHA can be traced back to the meeting in Renfrew in 1909, the official founding of the NHL and the establishment of the modern professional hockey league as we know it today is recognized as having taken place in Montreal in 1917.