When Did January 1 Become The First Day Of The New Year?
When Julius Caesar (100-44 B.C.) crafted the Julian calendar in 46 B.C., he moved the beginning of the year to January 1. Even after the introduction of the Gregorian calendar in 1582, January 1 continued to be recognized as the first day of the year in most places.
However, up until 1752, England and its American colonies started the new year with March 25, representing the spring equinox. (The equinox, which occurs each spring and fall, is the date on which the sun shines most directly on the equator and day and night are of roughly equal length). Under this system, March 24, 1700, was followed by March 25, 1701. In 1752, the British government declared that January 1 would begin the new year.
Source: Asimov, Isaac. Asimov on Numbers, p. 159.