When did Niagara Falls freeze completely over?

Most recently, it froze in 2014
http://www.dailymail.co.uk/news/article-2536278/Spectacular-photographs-moment-Niagara-Falls-FROZE-polar-vortex-saw-record-breaking-temperatures-tourist-mecca.html

This site says 1938.
http://www.overthefallstours.com/falls-trivia-answers.html

Another source: Before the installation of the ice-boom in 1964, the American side of the falls froze over in 1909, 1938 and 1949 because ice jams upstream reduced the water flow.
https://www.worldatlas.com/articles/does-niagara-falls-freeze-has-niagara-falls-frozen.html

The first and only time both the American falls and the Horseshoe Falls on the Canadian side fell silent was on the night of March 29, 1848, when an ice jam formed on Lake Erie near Buffalo blocking the water that flows along the Niagara River and over the falls, says Dave Phillips of Environment Canada. On six reported occasions (1883, 1896, 1904, 1909, 1936 and 1947), the water flow over American Falls has been totally blocked by ice and ceased to fall. But only once has this happened to the much larger Horseshoe Falls (originally known as the Canadian Falls): March 29-31, 1848, the Days Niagara Falls Went Dry.
Source: The Weather Almanac

Frozen solid almost never happens, there is usually a small trickle among the ice.

Yet, in 1911 it is possible that there was a major freezing.

http://www.snopes.com/photos/natural/niagarafalls.asp

The volume of water going over the Falls, the depth and speed of the water below the Falls also precludes freezing. The water will not be stopped or frozen solid. The installation of the ice boom at the mouth of Lake Erie, the building of the International water control dam (which regulates water flow) and milder winters have all but eliminated the possibility of the American Falls ever completely freezing over in modern times.

In 1997, the ice bridge was bigger than usual because several sections of the ice boom were knocked out in early winter during a storm. The American Falls have frozen over on six occasions since the keeping of records began. Each were attributed to ice jams that have actually curtailed the flow of the American Falls to mere trickles. The American Falls water flow was reduced to such an extent in 1909, 1936, 1938 and 1949 that it froze over.

https://www.niagarafrontier.com/faq.html