04/15/1846 About this date and throughout the spring of 1846, over 12,000 Mormons began a massive migration from Nauvoo, Illinois to Council Bluffs, Iowa. Source Citation Arthur M. Schlesinger, Jr., ed., The Almanac of American History (New York: Barnes & Noble Books, 1993), 251. Record Data Date Certainty Estimated Type Religion/Philosophy People Places Council Bluffs, IA Nauvoo, IL Images