What day of the week was May 31, 1866?

The day of the week May 31st, 1866 fell on was a Thursday.

In the Fenian Invasion of Canada the John O'Neill leads 850 Fenian raiders across the Niagara River at Buffalo, New York/Fort Erie, Ontario, as part of an effort to free Ireland from the United Kingdom. Canadian militia and British regulars repulse the invaders in over the next three days, at a cost of 9 dead and 38 wounded to the Fenian's 19 dead and about 17 wounded.