Early european explorers of
North America tried to time visits so that they arrived by
Saint John the Baptist's day (late June). This target was both practical (allowed exploration, plus a timely return) and was imbued with good luck. As a consequence, the original settlers named the first place of landing after this Saint. At one point there were three Saint John places in Eastern
Canada:
The too-many-Saint-Johns problem was partly behind the renaming business for
P.E.I.. If you're travelling in Eastern Canada, don't confuse
St. John's with
Saint John, unless you want trouble.