In Hancock County, Illinois, not far from the old Fort Madison ferry which led into the half-breed country of Iowa, the Mormons discovered a village of Commerce, once founded by a communistic settlement from which the business genius of Smith now purchased it on easy terms. It was occupied in 1839, renamed Nauvoo in 1840, and in it a new tabernacle was begun in 1841. From the poverty-stricken young clairvoyant of fifteen years before, the prophet had now developed into a successful man of affairs, with ambitions that reached even to the presidency at Washington. With a strong sect behind him, money at his disposal, and supernatural powers in which all faithful saints believed, Joseph could go far. Nauvoo had a population of about fifteen thousand by the end of 1840.

Coming into Illinois upon the eve of a closely contested presidential election, at a time when the state feared to lose its population in an emigration to avoid taxation, and with a vote that was certain to be cast for one candidate or another as a unit, the Mormons insured for themselves a hearty welcome from both Democrats and Whigs. A complaisant legislature gave to the new Zion a charter full of privilege in the making and enforcing of laws, so that the ideal of the Mormons of a state within the state was fully realized. The town council was emancipated from state control, its courts were independent, and its militia was substantially at the beck of Smith. Proselyting and good management built up the town rapidly. To an importunate creditor Smith described it as a "deathly sickly hole," but to the possible convert it was advertised as a land of milk and honey. Here it began to be noticed that desertions from the church were not uncommon; that conversion alone kept full and swelled its ranks. It was noised about that the wealthy convert had the warmest reception, but was led on to let his religious passion work his impoverishment for the good of the cause.

Here in Nauvoo it was that the leaders of the church took the decisive step that carried Mormonism beyond the pale of the ordinary, tolerable, religious sects. Rumors of immorality circulated among the Gentile neighbors. It was bad enough, they thought, to have the Mormons chronic petty thieves, but the license that was believed to prevail among the leaders was more than could be endured by a community that did not count this form of iniquity among its own excesses. The Mormons were in general of the same stamp as their fellow frontiersmen until they took to this. At the time, all immorality was denounced and denied by the prophet and his friends, but in later years the church made public a revelation concerning celestial or plural marriage, with the admission that Joseph Smith had received it in the summer of 1843. Never does Mormon polygamy seem to have been as prevalent as its enemies have charged. But no church countenancing the practice could hope to be endured by an American community. The odium of practising it was increased by the hypocrisy which denied it. It was only a matter of time until the Mormons should resume their march.

The end of Mormon rule at Nauvoo was precipitated by the murder of Joseph Smith, and Hyrum his brother, by a mob at Carthage jail in the summer of 1844. Growing intolerance had provoked an attack upon the Saints similar to that in Missouri. Under promise of protection the Smiths had surrendered themselves. Their martyrdom at once disgraced the state in which it could be possible, and gave to Mormonism in a murdered prophet a mighty bond of union. The reins of government fell into hands not unworthy of them when Brigham Young succeeded Joseph Smith.

Not until December, 1847, did Brigham become in a formal way president of the church, but his authority was complete in fact after the death of Joseph. A hard-headed Missouri River steamboat captain knew him, and has left an estimate of him which must be close to truth. He was "a man of great ability. Apparently deficient in education and refinement, he was fair and honest in his dealings, and seemed extremely liberal in conversation upon religious subjects. He impressed La Barge," so Chittenden, the biographer of the latter relates, "as anything but a religious fanatic or even enthusiast; but he knew how to make use of the fanaticism of others and direct it to great ends." Shortly after the murder of Joseph it became clear that Nauvoo must be abandoned, and Brigham began to consider an exodus across the plains so familiar by hearsay to every one by 1845, to the Rocky Mountains beyond the limits of the United States. Persecution, for the persecuted can never see two sides, had soured the Mormons. The threatened eviction came in the autumn of 1845. In 1846 the last great trek began.

The van of the army crossed the Mississippi at Nauvoo as early as February, 1846. By the hundred, in the spring of the year, the wagons of the persecuted sect were ferried across the river. Five hundred and thirty-nine teams within a single week in May is the report of one observer. Property which could be commuted into the outfit for the march was carefully preserved and used. The rest, the tidy houses, the simple furniture, the careful farms (for the backbone of the church was its well-to-do middle class), were abandoned or sold at forced sale to the speculative purchaser. Nauvoo was full of real estate vultures hoping to thrive upon the Mormon wreckage. Sixteen thousand or more abandoned the city and its nearly finished temple within the year.

Across southern Iowa the "Camp of Israel," as Brigham Young liked to call his headquarters, advanced by easy stages, as spring and summer allowed. To-day, the Chicago, Burlington, and Quincy railway follows the Mormon road for many miles, but in 1846 the western half of Iowa territory was Indian Country, the land of the Chippewa, Ottawa, and Potawatomi, who sold out before the year was over, but who were in possession at this time. Along the line of march camps were built by advance parties to be used in succession by the following thousands. The extreme advance hurried on to the Missouri River, near Council Bluffs, where as yet no city stood, to plant a crop of grain, since manna could not be relied upon in this migration. By autumn much of the population of Nauvoo had settled down in winter quarters not far above the present site of Omaha, preserving the orderly life of the society, and enduring hardships which the leaders sought to mitigate by gaiety and social gatherings. In the Potawatomi country of Iowa, opposite their winter quarters, Kanesville sprang into existence; while all the way from Kanesville to Grand Island in the Platte Mormon detachments were scattered along the roads. The destination was yet in doubt. Westward it surely was, but it is improbable that even Brigham knew just where.

The Indians received the Mormons, persecuted and driven westward like themselves, kindly at first, but discontent came as the winter residence was prolonged. From the country of the Omaha, west of the Missouri, it was necessary soon to prohibit Mormon settlement, but east, in the abandoned Potawatomi lands, they were allowed to maintain Kanesville and other outfitting stations for several years. A permanent residence here was not desired even by the Mormons themselves. Spring in 1847 found them preparing to resume the march.

In April, 1847, an advance party under the guidance of no less a person than Brigham Young started out the Platte trail in search of Zion. One hundred and forty-three men, seventy-two wagons, one hundred and seventy-five horses, and six months' rations, they took along, if the figures of one of their historians may be accepted. Under strict military order, the detachment proceeded to the mountains. It is one of the ironies of fate that the Mormons had no sooner selected their abode beyond the line of the United States in their flight from persecution than conquest from Mexico extended the United States beyond them to the Pacific. They themselves aided in this defeat of their plan, since from among them Kearny had recruited in 1846 a battalion for his army of invasion.

Up the Platte, by Fort Laramie, to South Pass and beyond, the prospectors followed the well-beaten trail. Oregon homeseekers had been cutting it deep in the prairie sod for five years. West of South Pass they bore southwest to Fort Bridger, and on the 24th of July, 1847, Brigham gazed upon the waters of the Great Salt Lake. Without serious premeditation, so far as is known, and against the advice of one of the most experienced of mountain guides, this valley by a later-day Dead Sea was chosen for the future capital. Fields were staked out, ground was broken by initial furrows, irrigation ditches were commenced at once, and within a month the town site was baptized the City of the Great Salt Lake.