Millerism founded by William Miller
The Millerites were the followers of the teachings of William Miller, who in 1831 first shared publicly his belief that the Second Advent of Jesus Christ would occur in roughly the year 1843–1844. Coming during the Second Great Awakening, his teachings were spread widely and grew in popularity, which led to the event known as the Great Disappointment.Origins
Miller was a prosperous farmer, a Baptist lay preacher, and student of the Bible living in northeastern New York.  He spent years of intensive study of symbolic meaning of the prophecies of Daniel, especially Daniel 8:14 (Unto two thousand and three hundred days; then shall the sanctuary be cleansed), the 2,300-day prophecy.Miller believed that the cleansing of the sanctuary represented the Earth's destruction by fire at Christ's Second Coming.  Using the year-day method of prophetic interpretation, Miller became convinced that the 2,300-day period started in 457 BC with the decree to rebuild Jerusalem by Artaxerxes I of Persia.  Simple calculation then indicated that this period would end about 1843.  In September 1822, Miller formally stated his conclusions in a twenty-point document, including article 15, "I believe that the second coming of Jesus Christ is near, even at the door, even within twenty-one years,—on or before 1843." This document remained private for many years.
Miller did eventually share his views, first to a few friends privately and later to some ministerial acquaintances.  Initially he was disappointed at the lack of response from those he spoke to.  "To my astonishment, I found very few who listened with any interest.  Occasionally, one would see the force of the evidence, but the great majority passed it by as an idle tale."Miller states that he began his public lecturing in the village of Dresden, Washington County, New York, some 16 miles from his home, on "the first Sabbath in August 1833."  However, as Sylvester Bliss points out, "The printed article from which this is copied was written in 1845.  By an examination of his correspondence, it appears that he must have begun to lecture in August 1831.  So that this date is a mistake of the printer or an error in Mr. Miller's memory."In 1832, Miller submitted a series of sixteen articles to the Vermont Telegraph—a Baptist paper.  The first of these was published on May 15, and Miller writes of the public's response, "I began to be flooded with letters of inquiry respecting my views, and visitors flocked to converse with me on the subject."  In 1834, unable to personally comply with many of the urgent requests for information and the invitations to travel and preach that he received, Miller published a synopsis of his teachings in a "little tract of 64 pages."  These he "...scattered, the most of them gratuitously, sending them in reply to letters of inquiry and to places which I could not visit."